Tap water in most developed countries is treated to kill pathogens and is safe in the sense that drinking it won't give you cholera. The treatment process — typically involving chlorination, sometimes chloramination, sometimes UV — is effective at its stated purpose.
What it doesn't do is remove the growing list of chemical contaminants that enter water sources from agriculture, industry, pharmaceutical use, and infrastructure. Regulatory frameworks for water contaminants are slow to update, expensive to test for, and set maximum contaminant levels based on single-compound assessments that don't account for combined exposure.
◈Key Facts
The contaminants that matter most
PFAS
PFAS enter water from industrial discharge, firefighting foam used at airports and military bases, and agricultural runoff from contaminated sludge used as fertiliser. They are essentially permanent once in a water source.
The EPA set advisory levels for several PFAS compounds in 2022, and maximum contaminant levels were proposed in 2023 — but regulatory implementation lags behind the science. Many municipal supplies still exceed advisory levels, and private well water is often unmonitored.
Lead
There is no safe blood lead level in children. Lead pipes were used extensively in water infrastructure until the 1980s and are still present in older homes in many countries. Lead doesn't come from water treatment facilities — it leaches into the water from pipes and fixtures as it travels to your tap, which is why filtration at the point of use (your tap) is the relevant intervention.
If you're in an older home (pre-1986 in the US, older in the UK and EU) and haven't had your water tested for lead, this is worth doing.
Chlorination byproducts
Chlorine is added to water to kill pathogens. When it reacts with naturally occurring organic matter in the water, it forms disinfection byproducts (DBPs) — primarily trihalomethanes (THMs) and haloacetic acids (HAAs). These are regulated, but at levels that reflect treatment practicality as much as health optimisation.
Long-term DBP exposure has been associated in epidemiological studies with increased bladder cancer risk. Showering in hot water (where DBPs volatilise and can be inhaled) may be a more significant exposure route than drinking for some people.
Nitrates
Nitrates from agricultural runoff are a significant contaminant in many water sources, particularly near intensive farming. Nitrates are of particular concern for infants and pregnant women — in infants, they can cause methaemoglobinaemia (blue baby syndrome). In adults, high nitrate intake is associated with increased colorectal cancer risk.
Microplastics
Microplastics have been detected in tap water, bottled water, and effectively all water sources globally. Research on health effects is in early stages but they have been found in human lung tissue, blood, and placentas. Some microplastics carry surface-adsorbed chemicals including endocrine disruptors. The filtration situation for microplastics is complicated — most standard filters don't address them well.
Filtering options
Reverse osmosis removes the widest range of contaminants — PFAS, lead, nitrates, most microplastics, chlorination byproducts, and most other dissolved contaminants. It also removes minerals, so remineralisation or using a system with a mineral filter stage is preferred. Under-sink systems are the most practical for drinking and cooking water.
Solid block activated carbon (not granulated carbon) removes chlorine, chlorination byproducts, PFAS, some pesticides, and many VOCs. Doesn't remove lead, nitrates, or most minerals. Counter-top pitcher filters (Brita) typically use granulated carbon and are significantly less effective than solid block.
Pitcher filters (basic) — primarily remove chlorine taste and some sediment. Not effective for PFAS, lead, or nitrates. Better than nothing, not sufficient if PFAS or lead are concerns.
For PFAS or lead concerns specifically, only reverse osmosis and certain certified solid block carbon filters (look for NSF/ANSI 58 certification for RO, NSF/ANSI 53 for lead on carbon filters) provide meaningful reduction.
Bottled water is not the answer
Bottled water is unregulated to a lower standard than tap water in most jurisdictions. It often contains microplastics shed from the bottle itself. It's expensive. And the environmental cost is significant. A good point-of-use filter on your tap is a better intervention than bottled water in almost every respect.