Nickel is a silvery white metal. It is found in most water, usually at the level of about one part per billion. Although it is a suspected carcinogen when inhaled, there is no evidence that it poses a threat when ingested orally. In some it produces allergic reactions.

The EPA has no proposed MCL for nickel.

Removal from water can be done by a strong acid cation exchanger. Activated carbon reduces nickel, and reverse osmosis removes 97 to 98%.