Well Water Contaminants

Contaminants by type

Each contaminant below sits under its main concern. Open one to see its levels, where it comes from, its health effects and what to do after a test.

Health, aesthetic and plumbing

These are the common well water contaminants we cover. They fall into three groups, and EPA treats each group differently. Knowing a contaminant's group tells you how much weight its standard carries and what a high level can mean for you.

Health. EPA's National Primary Drinking Water Regulations are legally enforceable primary standards and treatment techniques that apply to public water systems. For many contaminants they set a Maximum Contaminant Level (MCL), the highest level allowed in drinking water, and a health goal (MCLG), the level below which there is no known or expected risk to health. Lead and copper work differently: they are regulated by a treatment technique that requires systems to control how corrosive their water is, with an action level that triggers extra steps.

Aesthetic. EPA's secondary standards set non-mandatory levels for 15^[2] contaminants, and EPA does not enforce them. They cover aesthetic effects, such as undesirable tastes or odors, and cosmetic effects, which do not damage the body but are still undesirable. EPA says these contaminants can make water look cloudy or colored, or taste or smell bad. A sign like that is a reason to test, not an answer: our pages on a rotten-egg smell and brown well water explain what those signs of well water problems can and can't tell you.

Plumbing. The secondary standards also cover technical effects: damage to water equipment, or less effective treatment for other contaminants. Corrosive water can leave a metallic taste, corrode pipes and stain fixtures, and high total dissolved solids can leave hardness and deposits.

One contaminant, more than one benchmark. Some contaminants have both a health benchmark and a secondary standard. The list above puts each contaminant under its main concern, and each contaminant's page lists every benchmark we compare a result with and names what kind of benchmark it is.

If you have a private well. EPA says the quality of water from private wells is not regulated under the Safe Drinking Water Act or by most state governments. These standards do not bind your well, but they are the federal benchmarks our pages use to explain a lab result.