Contaminants
Every contaminant profile: where it comes from, how it behaves in water, how it is measured, what the limits are in each jurisdiction, and what actually removes it.
A family of several thousand synthetic fluorinated compounds whose carbon–fluorine bonds make them exceptionally persistent. They are mobile in groundwater, resistant to conventional treat…
A neurotoxic metal that almost never originates in source water. Lead in tap water comes from lead pipes, lead solder and brass fittings between the main and the tap, which is why it is on…
A naturally occurring metalloid that is the largest chemical mass-poisoning exposure in drinking water worldwide, principally through groundwater in the Bengal basin and parts of South and…
The definitive indicator of recent faecal contamination. E. coli is not usually the pathogen of concern itself; it is present in enormous numbers in faeces, survives in water for a similar…
The most widespread diffuse chemical pollutant of groundwater in intensively farmed regions. Nitrate is highly soluble and moves readily with water, so it accumulates in aquifers over deca…
A protozoan parasite whose oocysts are highly resistant to chlorine at the doses used in drinking water treatment. It is the classic case where disinfection alone is not enough, and physic…
Disinfection by-products formed when chlorine reacts with natural organic matter in water. They embody the central trade-off in drinking water treatment: the disinfection that prevents wat…
The most widely used drinking water disinfectant, and the intervention most responsible for the decline of waterborne disease in the twentieth century. A residual concentration is delibera…
Naturally present in many groundwaters and added deliberately to some public supplies for dental health. Fluoride is unusual among water constituents in having a narrow band between benefi…
A bacterium that causes Legionnaires’ disease and is a building water systems problem rather than a source water or mains problem. It proliferates in warm stagnant water in hot and cold se…
Plastic particles below five millimetres, now detected in tap water, bottled water and the wider environment. The exposure is real and well documented; the health significance is genuinely…
Blooms of cyanobacteria in nutrient-enriched lakes and reservoirs can release potent toxins, principally microcystins. Blooms are becoming more frequent as warmer water and continued nutri…
A large and changing group of regulated substances. European drinking water regulation is unusual in setting a uniform limit per individual pesticide regardless of its toxicity — a deliber…
Not a drinking water health concern, and the most important single pollutant in fresh water. Phosphorus is usually the nutrient limiting algal growth, so it is the one that determines whet…
A persistent toxic metal whose principal water concern is not drinking water concentration but bioaccumulation as methylmercury in fish.
Detected at nanogram concentrations in rivers and, at lower levels, in drinking water. The established environmental effects are real; the drinking water health significance at measured co…
Two oxidation states with entirely different toxicity. Trivalent chromium is an essential trace nutrient; hexavalent chromium is a carcinogen. Most regulation measures total chromium, whic…
Common in groundwater and in reservoirs that stratify in summer. Long treated as an aesthetic nuisance because it stains laundry and fittings black, manganese has attracted increasing atte…
When sulphide minerals exposed by mining meet water and air, they generate sulphuric acid, which then dissolves metals out of the surrounding rock. The process continues long after a mine …
A cumulative kidney toxin with a biological half-life of decades. Its principal exposure route is food rather than water, but contaminated irrigation water is how it gets into food.
Trichloroethylene and tetrachloroethylene from degreasing and dry cleaning. Denser than water, so they sink through aquifers rather than floating — which makes them among the hardest conta…
An intermediate in the nitrogen cycle, and considerably more acutely toxic than nitrate. Its presence in treated water usually indicates a problem in the distribution network rather than i…
Present naturally in acidic waters and introduced deliberately as a coagulant during treatment. Its regulation is an operational indicator — high aluminium means the coagulation process is…
Breakdown products of pesticides, which frequently outlast and out-travel the parent compound. Several are detected in groundwater decades after the parent pesticide was withdrawn.
Petrol, diesel and heating oil reaching groundwater from leaking tanks and spills. Detectable by taste and smell at concentrations far below health limits, which makes them unusually self-…
Chiefly a plumbing contaminant. Nickel leaches from chrome-plated taps and fittings, and concentrations are highest in the first water drawn after a period of standing.
Naturally occurring radioactivity in groundwater, mainly from uranium-bearing geology. For radon, the significant exposure is inhaling it after it comes out of the water, not drinking it.