Introduction
Most people never think about what's in their water until something goes wrong, a news story about a nearby town, a strange taste, a sick pet. But by then the conversation has already shifted from prevention to damage control.
This page isn't here to alarm you. It's here to give you a clear, honest picture of what can end up in household water, what that means for the people drinking it, and what it means for the food you're growing. Because whether you're filling a glass or watering a garden bed, the quality of that water matters more than most people realise.
You don't need a chemistry degree to understand this. Everything here is written to be as simple or as detailed as you want it to be. Skim the surface or go deep, the information meets you where you are.
Context
How Contaminants Get Into Your Water
Water doesn't arrive at your tap in the same state it left the sky. By the time it reaches you it has traveled through soil, rock, reservoirs, treatment facilities, and a network of pipes, and at every stage something can enter it.
At the source
Water begins as rain or snowmelt. As it moves through the ground it picks up whatever is there: minerals from rock, runoff from agricultural land, discharge from industrial sites. Surface water like rivers and lakes is especially exposed to what happens on the land around it. Groundwater drawn from wells tends to be more naturally filtered but can still carry dissolved minerals and chemicals that have leached down over years or decades.
At the treatment stage
Municipal water is treated before it reaches you: filtered, disinfected, pH balanced. This removes a lot but not everything. And the disinfection process itself introduces a category of byproducts that wouldn't be there otherwise. Treatment is a meaningful layer of protection, not a guarantee of purity.
In the pipes
This is the stage that surprises people most. Water can leave a treatment facility in good condition and still pick up contaminants on the last stretch to your tap, because the pipes it travels through are part of the system too. Older pipes, especially those made of lead or joined with lead solder, can leach directly into the water passing through them, and the longer that water sits still inside them, overnight or across a working day, the more it tends to pick up. The service line that connects a home to the water main is a common culprit, and responsibility for it is often divided between the utility and the household in ways that are not obvious from the tap.
The age of your home and your neighbourhood's infrastructure matters here more than most people expect. In homes built before 1986 in the US, or before 1970 in the UK, lead pipework and lead solder are common enough to be worth testing for specifically rather than assuming either way. Even where the pipes themselves are not lead, older galvanised steel and some brass fittings can contribute metals of their own. None of this is a reason for alarm, since the fix is often straightforward once you know what you are dealing with, whether that means running the tap briefly to clear standing water or replacing a single old fixture or service line. Testing is the only way to be sure, because lead in particular has no taste, colour, or smell to warn you it is there. One habit matters more than most here: because lead dissolves more readily in hot water and can build up in a water heater over hours of standing, water for drinking, cooking, or infant formula is best drawn from the cold tap rather than the hot.
At the well
If you're on a private well, none of the municipal treatment applies. What comes out is what's in the ground around you, and that varies enormously depending on your location, local geology, and what activities have taken place nearby. Well owners carry full responsibility for knowing and managing what's in their water.
For home growers
Everything above applies to your garden too. If contaminants are present in your water supply they go into the soil every time you water, and they accumulate over time. Some plants absorb certain contaminants more readily than others. This isn't a reason to stop growing, it's a reason to know your water.
The Contaminants
What Can Be in Your Water
Each category below can be opened to reveal individual contaminants. Every entry shows a glance summary up front. Expand further for sources, health effects, and notes for home growers.
Heavy metals are naturally occurring elements that become a problem in water when they appear in concentrations the body can't handle. They don't change the way water looks, smells, or tastes, which makes them easy to overlook and important to test for.
Lead rarely travels from the treatment facility to your tap. In most cases it enters the water after it arrives, leaching from lead pipes, lead solder, or brass fittings inside your home or building. Homes built before 1986 are most likely to have lead-containing plumbing, but even newer homes can have fixtures that contribute small amounts. The problem is especially pronounced when water sits in pipes for several hours, which is why running the tap for a minute or two before using it for drinking or cooking is a simple precaution worth taking.
Lead has no safe level in drinking water. The EPA has set a Maximum Contaminant Level Goal for lead at zero, acknowledging that no amount is considered safe. Its effects are most serious in children, where even low-level exposure interferes with brain development, attention, and learning. In adults, long-term exposure is linked to kidney damage and elevated blood pressure.
Lead is a real concern in soil. It binds tightly to soil particles and accumulates over time. Leafy vegetables and root vegetables tend to absorb more than fruiting crops like tomatoes or peppers. If your water has lead, it is going into your garden soil every time you irrigate.
Arsenic gets into water primarily through natural rock and soil, though agricultural chemicals and industrial activity can also contribute. Arsenic has been detected in water utilities serving tens of millions of Americans, and well water is particularly vulnerable since it draws directly from groundwater where arsenic deposits can be significant.
The EPA's current Maximum Contaminant Level for arsenic is 10 parts per billion, though some research suggests effects on children's development at levels as low as 5 parts per billion. Arsenic in drinking water is associated with bladder cancer, and chronic exposure also affects the lungs, skin, and nervous system. Chronic arsenic toxicity causes skin manifestations and has been linked to cognitive dysfunction and neurological problems.
Arsenic accumulates in soil and is taken up differently depending on what you grow. Concentrations are highest in leafy greens, lower in root vegetables, and significantly lower in tomato fruit.
Mercury exists in several forms, and the type matters for how it behaves in the body. In water it is most often found as inorganic mercury, which enters through industrial discharge, mining activity, and atmospheric deposition settling into surface water over time.
Mercury in drinking water has been causally linked to chronic kidney disease. It also affects the central nervous system and liver, with developing fetuses and young children being most vulnerable.
Mercury in irrigation water is less likely to accumulate in the edible parts of most vegetables than lead or arsenic, but it remains a concern in soil health over the long term.
Trivalent chromium (chromium-3) is an essential trace nutrient. Hexavalent chromium (chromium-6) is a byproduct of industrial processes, enters water through industrial discharge and improper waste disposal, and is a known carcinogen. Tens of millions of Americans are exposed to hexavalent chromium in their drinking water, with no federal limit currently established specifically for it. The EPA regulates total chromium but not the hexavalent form separately, which many researchers consider insufficient.
Chromium in drinking water is considered a risk factor for liver and kidney injury as well as cancer development.
Cadmium is not naturally abundant in drinking water but can appear where industrial contamination has occurred or where older infrastructure is degrading.
Long-term cadmium exposure can result in chronic renal failure, anemia, high blood pressure, and osteoporosis. It is also classified as a carcinogen.
Cadmium is one of the more concerning metals for growers because certain vegetables, particularly leafy greens and root vegetables, take it up readily from soil. Prolonged irrigation with contaminated water leads to increases in cadmium levels in soil over time, which are then taken up by the vegetables grown in those soils.
Biological contaminants are living organisms, or remnants of them, that can cause illness when ingested. Unlike heavy metals, which accumulate in the body over time, biological contaminants tend to cause acute illness. Municipal treatment handles most of them effectively, but not all, and well water has no such protection by default.
Bacteria enter water primarily through human and animal waste. The most well-known indicator is E. coli, which signals fecal contamination is present. Other bacteria of concern include Helicobacter pylori and members of the Salmonella family. The greater risk is in private wells, where contamination from nearby livestock, septic systems, or surface runoff can introduce bacteria with no treatment step to catch it.
Health effects range from mild stomach upset to severe diarrhea, dysentery, and in some cases typhoid fever.
Bacteria in irrigation water can settle on the surface of vegetables, particularly leafy greens eaten raw. Watering at the base of plants and washing produce thoroughly reduce this risk meaningfully.
Waterborne viruses enter the supply through fecal contamination of source water. Viruses of concern include Hepatitis A, Norwalk-type viruses, rotaviruses, and enteroviruses. They are extremely small, which means standard filtration alone may not remove them. Disinfection with chlorine or UV light is what actually neutralises them in treated supplies.
Waterborne viruses can cause infectious diseases ranging from gastroenteritis to hepatitis. Well water users should be aware that standard ceramic or sediment filters do not reliably remove viruses. UV treatment or chemical disinfection is necessary when viral contamination is a concern.
Giardia is a protozoan that forms hardy cysts capable of surviving in cold water for months. It can be found in water following contamination by the feces of humans or other animals. Surface water sources like rivers, streams, and lakes are most vulnerable, particularly in areas with high wildlife activity or nearby livestock.
Giardiasis brings stomach cramping, bloating, nausea, and prolonged diarrhea. Rarely life-threatening in healthy adults but can be serious in young children, elderly people, and those with weakened immune systems. Critically, Giardia produces cysts that are extremely resistant to chlorine-based disinfectants, meaning physical filtration is required to remove it reliably.
Cryptosporidium forms tough protective shells that make it resistant to chlorine, the primary tool used in municipal treatment. It is transmitted through human or animal feces into water. Municipal systems serving surface water are required to use filtration specifically to address it. Well owners and anyone drawing from surface water without filtration are at the highest risk.
For people with compromised immune systems, including infants, the elderly, those with HIV/AIDS, and transplant recipients, cryptosporidiosis can become life-threatening. In healthy adults it usually causes several days of severe gastrointestinal illness.
Both Giardia and Cryptosporidium can be present in untreated water used for irrigation. They do not infect plant tissue but can persist on the surface of produce. Anything grown close to the ground and eaten raw warrants careful washing.
This category covers chemicals that enter water primarily through agricultural activity and land use. For well owners and home growers in or near farming areas, this section is especially relevant.
Pesticides travel primarily through runoff after rain events and through slow downward movement into groundwater over time. The most commonly detected herbicide in water supplies is atrazine, used widely on corn crops. Glyphosate is also frequently detected. When pesticides are found in water supplies they are rarely at concentrations high enough to cause acute effects. The concern is primarily chronic, meaning problems that develop from long-term exposure to relatively low concentrations.
Chronic exposure has been linked to cancer, reproductive disorders, endocrine disruption, and neurological impairment. Endocrine disruption is particularly notable because certain pesticides interfere with the body's hormone signalling even at very low concentrations.
Pesticide runoff from neighbouring properties or nearby farmland can reach your garden through shared groundwater or surface drainage. If you are in an agricultural area, well water should be tested.
Nitrates come from fertilisers, animal waste, and septic systems. They dissolve easily in water and move readily through soil into groundwater, making them a consistent and widespread problem in farming regions. Levels can be dangerously high in agricultural areas where fertilisers, animal waste, and septic tank runoff are present.
The maximum contaminant level before nitrates become a health concern is 10 milligrams per liter. Above that threshold the primary concern is methemoglobinemia, known as blue baby syndrome, where nitrates interfere with the blood's ability to carry oxygen. High nitrate levels pose serious health problems especially for infants and pregnant women. In adults, long-term elevated exposure has been associated with increased cancer risk.
In small amounts, nitrates feed plants as a form of nitrogen. At high levels they can affect plant health and accumulate in leafy vegetables, particularly spinach and lettuce, which absorb nitrates more readily than most crops. Well water in agricultural areas should be tested annually.
Synthetic chemicals that enter water through industrial activity, manufacturing, and military operations. These were created, widely used, and in many cases released into the environment before their persistence and health effects were fully understood.
PFAS is not a single chemical but a group of thousands of related synthetic compounds used to make products resistant to water, heat, and stains. They have been used since the 1940s in products ranging from non-stick cookware and stain-resistant fabrics to food packaging and firefighting foam. PFAS contamination in drinking water primarily comes from aqueous film-forming foam, a firefighting foam developed during the Vietnam War and widely used by military organisations, airports, and fire stations globally since the 1960s.
Research has concluded with a high degree of certainty that PFAS contribute to thyroid disease, elevated cholesterol, liver damage, and kidney and testicular cancer. Babies exposed in utero face increased likelihood of lower birth weight. PFAS exposure has also been linked to reduced vaccine efficacy and developmental delays in children. Because PFAS resist breakdown and are only slowly excreted, they accumulate in human tissues over time.
The EPA set enforceable limits for six PFAS chemicals in drinking water in 2024. Those regulations were partially rolled back in May 2025. The situation remains in flux, and the gap between what science indicates is harmful and what is currently regulated remains wide.
PFAS accumulate in soil over time and can be taken up by certain crops. Leafy and root vegetables tend to absorb more than fruiting crops. Standard pitcher filters and most common home filtration systems do very little to remove PFAS. Reverse osmosis is the option that works, see the filtration section.
Volatile organic compounds are carbon-based chemicals that evaporate easily at room temperature. In water, the ones of most concern are industrial solvents like trichloroethylene (TCE) and tetrachloroethylene (PCE), used historically in dry cleaning, metal degreasing, and manufacturing. They enter groundwater through improper disposal, leaking underground storage tanks, and contaminated industrial sites, and can persist and spread for decades.
Chemical contaminants in drinking water have been associated with cancer, cardiovascular disease, neurological disease, and miscarriage. TCE in particular is a known human carcinogen linked to kidney cancer and non-Hodgkin's lymphoma. Well water near industrial areas or former industrial sites carries the highest risk.
These contaminants are not present in source water. They are created during the treatment process itself, when disinfectants like chlorine react with naturally occurring organic matter in water. The diseases prevented by treating water far outweigh the risks posed by byproducts, but it is worth understanding what is being traded and what can be done about it at home.
When chlorine is added to water containing natural organic matter, a chemical reaction produces trihalomethanes. The four regulated THMs are chloroform, bromoform, dibromochloromethane, and bromodichloromethane. Chloroform and bromodichloromethane are listed as reasonably anticipated to be human carcinogens by the National Toxicology Program.
Epidemiological studies have consistently found an association between consumption of chlorinated drinking water and an increased risk of bladder cancer. Long-term exposure above regulated limits has also been linked to liver, kidney, and central nervous system effects. Disinfection byproducts also increase the risk of complications during pregnancy, including miscarriage, cardiovascular defects, and low birth weight.
Water system engineers intentionally maintain a chlorine residual in distribution pipes because it keeps water safe from bacteria and viruses as it travels to your home. This is a genuine tradeoff between safety from microbes and safety from THMs. For most people the microbe risk is the larger one. THMs are volatile, so letting water sit uncovered or using an activated carbon filter reduces them significantly.
Haloacetic acids form through the same process as THMs but behave differently in water. They do not evaporate, so letting water sit does nothing to reduce them. Together, trihalomethanes and haloacetic acids make up roughly 50 to 75 percent of total halogenated disinfection byproducts in drinking water.
Research indicates that haloacetic acids, particularly brominated haloacetic acids, are more carcinogenic than trihalomethanes. Six specific haloacetic acids are individually listed as reasonably anticipated to be human carcinogens. The EPA currently regulates a group of five known as HAA5, leaving others unmonitored. Activated carbon filtration and reverse osmosis both reduce HAAs effectively.
Some municipal water systems have shifted from chlorine to chloramines, a combination of chlorine and ammonia, partly to reduce THM and HAA formation. Chloramines do produce fewer of those specific byproducts, but they generate a different set entirely, including nitrosamines, some of which are considered more toxic than what they replaced. The science on chloramine byproducts is still developing.
Chloramines are harder to remove at home than chlorine. Standard carbon filters reduce chlorine readily but are less effective against chloramines. Catalytic carbon filters handle chloramines better than standard activated carbon and are worth specifying if your municipal water uses chloramine disinfection.
These are substances deliberately introduced into the water supply as part of the treatment process. What sets this category apart from every other on this page is that they enter your water by design, not through industrial accident, geological processes, agricultural runoff, or aging infrastructure. That makes them a different kind of conversation, one about weighing collective public health benefits against individual choice and emerging risk.
Community water fluoridation has been practiced in the United States since the mid-20th century with the primary goal of reducing tooth decay. Studies have consistently shown that community water fluoridation can prevent up to 25 percent of tooth decay in children and adults, and the CDC has recognised it as one of the ten greatest public health achievements of the 20th century. Fluoride works both before and after teeth erupt: early exposure strengthens enamel during development, while ongoing consumption helps rebuild weakened enamel and reverse early decay. The US Public Health Service recommends a fluoridation level of 0.7 milligrams per liter.
The safety of water fluoridation has been questioned for decades, but recent research has brought the conversation into sharper focus. In August 2024, the National Toxicology Program published a systematic review concluding, with moderate confidence, that higher estimated fluoride exposures are consistently associated with lower IQ in children, specifically at drinking water concentrations exceeding the World Health Organization guideline of 1.5 mg/L.
The NTP defined this higher exposure as more than 1.5 milligrams per liter, which is double the level used for water fluoridation in the United States. The report does not directly evaluate community water fluoridation at 0.7 mg/L, and there were insufficient data to determine whether that lower level has a negative effect on children's IQ.
In September 2024, a US District Court ruled that water fluoridation at the recommended level of 0.7 mg/L posed an unreasonable risk of reducing IQ in children and ordered the EPA to initiate rulemaking to address that risk. The EPA appealed the ruling, and in May 2026 the US Court of Appeals overturned the lower court decision, citing judicial overreach. Separately, the EPA committed in April 2025 to an accelerated review of fluoride science under the Safe Drinking Water Act, releasing its preliminary assessment plan for public comment in early 2026, which could still inform future regulatory changes. The situation remains active and evolving.
At high concentrations above 4.0 mg/L, long-term fluoride exposure is associated with bone disease including painful and brittle bones in adults, and dental fluorosis, yellow or brown discoloration and pitting of the teeth, in children. These effects are well established and are the basis for the EPA's maximum contaminant level.
This is one of the genuinely contested areas in water science. The dental health benefits of fluoridation are backed by decades of public health data. The neurodevelopmental concerns are supported by a growing body of research but remain debated in terms of whether the levels used in US water supplies are the cause. Determining the optimal concentration of fluoride in water to minimise potential harm while maximising dental health benefits has been one of the most hotly debated subjects in public health over the past half-century. What this page can offer is the honest picture: the benefits are real, the questions are real, and the science is still developing.
Fluoride can cause visible injury to plants as well as reduce growth rate. Fluoride toxicity affects germination, growth, photosynthesis, and yield. Sensitive plants irrigated with fluoridated water can develop fluoride toxicity that results in tip burn and necrotic spots on leaves. Not all plants are equally affected, some are far more sensitive than others. If you notice unexplained leaf tip browning or spotting, fluoride in your irrigation water is worth investigating. Reverse osmosis removes fluoride effectively. Collecting rainwater for irrigation is another practical option and sidesteps the issue entirely.
Standard activated carbon filters do not remove fluoride. Reverse osmosis is the most effective home option, removing fluoride reliably. Certain ion exchange resins specifically designed for fluoride removal also work. If removing fluoride is a priority for your household, RO is the practical choice, see the filtration section for more detail.
These contaminants originate primarily from geology, the rocks, soils, and minerals that water passes through on its way to your tap or well. In some cases aging infrastructure plays a role too, but unlike the industrial and chemical categories, no deliberate manufacturing or disposal is required for them to appear. Their presence depends largely on where you live and what lies beneath the ground around you.
Uranium is a naturally occurring radionuclide that decays over time and forms radium. Radium breaks down further to form the radioactive gas radon. All three are naturally present in rocks and soils and can dissolve into groundwater. The most common radionuclides in water are radon, uranium, and radium, which are often found in granite or limestone. Areas with these rock formations are more likely to have groundwater with radioactive elements at elevated levels. Mining activity and oil extraction can also elevate concentrations in affected regions. In general, surface water does not contain radionuclides at levels of concern. Groundwater drawn from wells is where the risk is most significant.
Radium is a health hazard when ingested. A portion of what is consumed may accumulate in bone, and over time this increases the risk of bone cancer, leukemia, and lymphoma. Chronic uranium exposure is associated with kidney damage as well as cancer risk. Radon in water is a particular concern not just from drinking but from inhalation, radon off-gasses from water as it pours from faucets and showerheads and enters the air inside your home, where the primary health risk is lung cancer. The EPA's legal limits for radionuclides in drinking water apply to municipal systems. Well water is unregulated and untested unless the owner arranges it.
Radium is effectively removed by ion exchange and reverse osmosis. Uranium is removed by reverse osmosis and certain ion exchange resins. Radon in water requires whole-house treatment since the concern is off-gassing throughout the home, aeration systems are the most common approach. Standard carbon filters do not reliably remove radionuclides. If you are on a well in a granite or limestone region, or near areas with a history of uranium mining, testing for radionuclides is worth doing.
Asbestos enters drinking water through two pathways. The first is natural erosion of asbestos-containing rock and soil releasing fibers into groundwater. The second, and more common, is aging infrastructure. Millions of miles of asbestos-cement pipes were installed across the United States between the 1930s and 1980s. As those pipes corrode and break down, they shed fibers directly into the water flowing through them. The EPA has set a maximum contaminant level of 7 million fibers per liter for fibers longer than 10 micrometers. When that level is exceeded, water suppliers are required to notify customers within 30 days.
The health picture for ingested asbestos in water is genuinely less clear than for inhaled asbestos. The EPA and WHO acknowledge potential health risks, and asbestos in water has been associated with benign intestinal polyps and gastrointestinal cancers including peritoneal mesothelioma. However, Health Canada and the WHO have both concluded there is no consistent, convincing evidence that asbestos ingested through drinking water is harmful at typical exposure levels. This is one area where the science is less settled than for other contaminants on this page, and it is worth noting honestly rather than overstating the risk.
Standard water treatment effectively removes asbestos fibers. For home filtration, reverse osmosis and ceramic filters physically block asbestos fibers by size. If you are concerned about asbestos in your water, particularly if you live in an older area with known asbestos-cement infrastructure, a certified laboratory test can confirm whether levels are a concern.
Substances that have been present in water for some time but are only recently being detected, measured, and studied at scale. They are not yet fully regulated, which does not mean they are harmless. It means detection methods are new and regulation tends to follow science with a significant delay.
Microplastics are fragments of plastic smaller than five millimeters, created as larger plastics break down in the environment. They enter water through runoff, synthetic clothing fibers released during washing, degrading plastic infrastructure, and plastic packaging. In April 2026, the EPA elevated microplastics to its Contaminant Candidate List for the first time, unlocking focused research and potential future regulation.
Tiny fragments of plastic have been found in nearly every organ in the body, including the brain and lungs. Research is still developing. What is known is that some microplastics carry other contaminants with them, including PFAS and pesticides that adsorb onto their surface, meaning they may be a delivery mechanism for other harmful substances.
Microplastics in irrigation water can enter soil and have been detected in plant tissue, including root vegetables and leafy greens. The long-term implications for food safety are an active area of research. Standard pitcher filters do not remove microplastics reliably. Reverse osmosis is currently the most effective home option.
Every medication excreted by a human or animal, and every pill flushed or washed down a drain, enters the wastewater system. Conventional sewage treatment was not designed to remove pharmaceutical compounds, and many pass through largely intact. The EPA has released human health benchmarks for 374 pharmaceuticals, signalling how widespread the presence of these substances is expected to be.
Concentrations found in drinking water are generally very low. The concern is less about acute effects and more about long-term, chronic exposure to mixtures of compounds. Hormones and endocrine-disrupting compounds can influence biological systems at very low concentrations. Antibiotic residues in water are also contributing to the growing problem of microbial resistance to antibiotics.
For Home Growers
If You're Growing Food
Everything in the contaminants section applies to your garden. Water doesn't stop being what it is when it leaves the tap and enters a hose. Whatever is in it goes into your soil, and from there into the plants you eat. This section looks at the question from the water side; for the same ground approached from the garden, including how irrigation water affects soil biology over a season, see the irrigation section on the companion Growing Healthy Gardens guide.
How contaminants move
Contaminants in irrigation water enter the soil with every watering. Some bind tightly to soil particles and accumulate there over time. Others move more freely and can be taken up directly through plant roots into the edible parts of what you grow. The two factors that matter most are what you are growing and what specific contaminant is present.
What you grow makes a difference
Leafy vegetables such as spinach and lettuce are particularly prone to accumulating high concentrations of heavy metals because of their high transpiration rates. Fruiting vegetables generally exhibit lower metal accumulation. Root crops sit in direct contact with soil and are more susceptible to direct uptake.
As a general guide, the safest crops to grow in uncertain conditions are fruiting vegetables: tomatoes, peppers, squash, cucumbers, beans, and corn. Cornell's Waste Management Institute lists the least suitable crops as leafy greens, brassicas like broccoli and cauliflower, and root crops.
Contaminant notes for growers
Lead binds strongly to soil particles and stays near the surface. Adding compost to soil with elevated lead levels has been shown to reduce lead concentration in Swiss chard by up to 59 percent and in carrots by up to 20 percent.
Arsenic moves more readily into above-ground plant parts. Concentrations are highest in leafy greens, lower in root vegetables, and significantly lower in tomato fruit.
Cadmium is mobile in soil and taken up readily. Lettuce has among the highest capacity of any vegetable for accumulating cadmium. Crop selection matters more than washing as a protective measure.
PFAS in irrigation water is a newer concern. Leafy and root vegetables tend to take up more than fruiting crops. Practices that build soil health, including adding compost and minimising disturbance, tend to reduce PFAS uptake by increasing binding to soil particles.
Practical steps
- Test your irrigation water. If you are on a well, this is especially important.
- Build your soil. Compost is one of the most effective tools available for reducing contaminant availability to plant roots.
- Choose your crops with intention. When water or soil quality is uncertain, lean toward fruiting vegetables.
- Consider raised beds with clean imported soil if contamination in your area is a known concern.
- Wash produce thoroughly. Peeling root vegetables removes significantly more contamination than washing alone.
- Water at the base of plants rather than overhead to limit direct contamination of leaf surfaces.
Filtration
What Filters Actually Do
No single filter does everything. Each technology works by a specific mechanism, and each mechanism has specific strengths and gaps, which is why the honest answer to what makes the best water filter is always another question: best for removing what. A carbon filter that transforms the taste of chlorinated tap water may do almost nothing for dissolved metals, while a system that strips out nearly everything can also remove minerals you had no reason to take out, and cost far more to run. A filter only works while its media is fresh, so whatever you choose is a commitment to replacing it on schedule rather than a one-time fix. Knowing which technology addresses which class of contaminant is what lets you make an informed decision rather than a marketed one. A study of scores of household filters shows how wide the gap can be: under-sink reverse osmosis and two-stage systems removed PFAS almost completely, whereas ordinary activated-carbon pitchers and faucet filters were inconsistent, and a few whole-house carbon systems actually raised PFAS levels in the treated water.
The right filter therefore depends on what you are actually trying to remove, and that depends on knowing what is in your water in the first place. Testing before filtering is the more rational sequence, even though most people do it the other way around, buying a filter first and hoping it happens to match the problem. It is worth being clear about the goal before spending anything, because a filter chosen to fix a taste is not necessarily the one that removes a health risk you cannot taste at all. The types below are grouped by mechanism, with what each one does and does not handle, so you can match the filter to your water rather than to the marketing on the box.
The filter types
The most common filtration technology in home use. Works through adsorption, where contaminants bond to the enormous internal surface area of the carbon material. Highly effective at removing chlorine, volatile organic compounds, pesticides, herbicides, and improving taste and odour. Does not reliably remove dissolved inorganics like heavy metals, nitrates, arsenic, or PFAS. Does not kill or remove biological contaminants. Note: catalytic carbon handles chloramines better than standard activated carbon and is worth specifying if your municipal water uses chloramine disinfection.
The broadest-spectrum home filtration technology available. Forces water through a semi-permeable membrane with pores so small that most dissolved contaminants cannot pass through. Removes lead, arsenic, nitrates, heavy metals, PFAS (95–99%+), microplastics, bacteria, viruses, and pharmaceuticals. Most RO systems include carbon pre-filters and post-filters, making them a combined solution. Tradeoffs: produces wastewater in the process, removes beneficial minerals (remineralisation filters available), and membranes require regular replacement. Available as under-sink, countertop, or whole-house systems.
Kills bacteria, viruses, and protozoa by disrupting their DNA. Does not remove dissolved solids, chemicals, or any non-biological contaminants. Best understood as a targeted tool for biological contamination, most valuable for well water users. Should be paired with other filtration for chemical concerns. RO alone is not a primary disinfectant and should be combined with UV when biological contamination is a concern.
Use porous ceramic material to physically block bacteria, sediment, and protozoa including Giardia and Cryptosporidium. Do not remove viruses and do not address chemical or dissolved contaminants. Durable, low-maintenance, and often used in gravity-fed systems where electricity is unavailable.
Works by swapping unwanted ions in water for less harmful ones using a charged resin. Can target arsenic, nitrates, fluoride, sulfates, and heavy metals depending on configuration. Water softeners are the most common form. Does not address biological contaminants or most organic chemicals.
What works for what
| Contaminant | Ion Exchange | Ceramic | UV | Carbon | Reverse Osmosis |
|---|---|---|---|---|---|
| Radionuclides | Yes* | No | No | No | Yes |
| Asbestos | No | Yes | No | No | Yes |
| Fluoride | Yes* | No | No | No | Yes |
| Lead | Some | No | No | Partial* | Yes |
| Arsenic | Yes* | No | No | No | Yes |
| Heavy Metals | Some | No | No | Some* | Yes |
| Bacteria | No | Most | Yes | No | Yes |
| Viruses | No | No | Yes | No | Yes |
| Giardia / Crypto | No | Yes | Yes | No | Yes |
| Pesticides | No | No | No | Yes | Yes |
| Nitrates | Yes* | No | No | No | Yes |
| PFAS | No | No | No | Partial* | Yes |
| THMs | No | No | No | Yes | Yes |
| HAAs | No | No | No | Yes | Yes |
| Microplastics | No | Some | No | Partial* | Yes |
| Pharmaceuticals | No | No | No | Some | Yes |
| VOCs | No | No | No | Yes | Yes |
* Certified filters only. Look for NSF/ANSI 53 for lead, NSF P473 for PFAS, NSF/ANSI 244 for microplastics, and NSF/ANSI 58 for reverse osmosis systems. Not all filters of the same type perform equally.
For home growers: filtering irrigation water
Most home filtration systems are designed and sized for drinking water. Filtering irrigation water at volume is a different challenge.
- A whole-house carbon or RO system addresses contaminants at the source before water reaches any tap or hose bib.
- An outdoor carbon block filter on the garden hose bib reduces chlorine, chloramines, pesticides, and some heavy metals at low cost. It will not address PFAS, nitrates, or arsenic.
- If PFAS or nitrates in irrigation water are a specific concern, collecting rainwater for garden irrigation is a practical alternative where regulations permit.
A note on sediment
Sediment itself, sand, silt, rust particles, and fine debris, is not chemically harmful, but it matters for two reasons. First, it carries other contaminants. Heavy metals, bacteria, and pesticide residues can all adsorb onto sediment particles and travel with them through your water supply. Second, sediment damages filters. It clogs carbon and RO membranes, dramatically shortening their effective life and reducing performance. If your water runs discoloured after heavy rain or carries visible particles, a sediment pre-filter installed before your main filter protects the system and keeps everything downstream working as intended.
Know Your Water
Knowing What's in Yours
Everything on this page describes what can be in water. What is actually in yours depends on where you live, how old your home is, what your local land has been used for, and whether you are on municipal supply or a private well. The only way to know for certain is to look.
If you are on municipal water
Your water utility is required by law to test your water regularly and publish the results. This document is called an Annual Water Quality Report, sometimes referred to as a Consumer Confidence Report. To find yours, search your water utility's name alongside "water quality report" or visit the EPA's website. Your utility name is usually on your water bill.
The report covers what leaves the treatment facility, not necessarily what arrives at your tap. Lead may not be detectable at the plant but can still be present at your faucet due to your home's plumbing. The report also covers regulated contaminants only. PFAS regulation is recent and incomplete, emerging contaminants like microplastics are not yet included, and not every pesticide or industrial chemical is on the testing list. Reading the report is a starting point, not the full picture.
If you are on a private well
No government agency tests your well water. That responsibility belongs entirely to you. Well water quality can change over time as land use around you changes, as water tables shift, and as your well infrastructure ages. Annual testing for bacteria and nitrates is a reasonable baseline. If you are in an agricultural area, testing for pesticides and arsenic makes sense. If you are near industrial sites or military installations, PFAS testing is worth doing. Local health departments and university extension programs in many areas offer guidance and testing services at low cost.
Getting independent testing done
Look for a laboratory certified by your state for drinking water analysis. You can search for certified labs through your state's environmental or health agency website. Avoid testing kits sold at hardware stores for anything beyond a very basic initial screen. When choosing what to test for, let your situation guide you: an older home warrants a lead test; a rural well near farmland warrants nitrate and pesticide testing; a location near industrial activity warrants PFAS and VOC testing. Results from a certified lab will include detected concentrations alongside EPA maximum contaminant levels for comparison.
Water quality is not a crisis to panic about. For most people in most places, tap water is safe to drink and use every day. The goal of this page has never been to frighten you. It has been to give you an honest, detailed picture of what can be present, what it means, and what you can actually do about it.
Knowledge scales with effort. Read your annual water quality report. Get your well tested once a year. Choose a filter that matches what your water actually contains. Grow fruiting crops if your soil or water quality is uncertain. None of these steps are complicated or expensive, and any one of them puts you ahead of where most people are.
Your situation is specific. The most useful thing this page can do is point you toward your own water, your own soil, your own home. General information about contaminants is a framework, not a verdict. What matters is what is in your water, which is something you can find out.
For home growers, the connection between water quality and food safety is real and underappreciated. Watering thoughtfully, building healthy soil, choosing crops wisely, and knowing what is in your irrigation water are habits that compound over time in the best way possible.