Foaming is usually caused by synthetic organic chemicals called surfactants. Surfactants, commonly found as ingredients in household detergents, may contaminate sources of drinking water though household or industrial waste disposal. Foaming agents cause frothing at and above concentrations of 1 mg/L and are associated with an oily, fishy, or perfume-like taste (Secondary Drinking Water Regulations: Guidance for Nuisance Chemicals; EPA810-K-92-001; July 1992).
Ingestion of doses above 50 mg/L, assuming a two liter per day consumption, may cause gastrointestinal irritation. EPA set a secondary maximum contaminant level of 0.5 mg/L to prevent the occurrence of visible foam. However, since the presence of foaming substances in drinking water is an indicator of sewage contamination, the appearance of visible foam should be investigated immediately (National Secondary Drinking Water Regulations; EPA570-9-76-000; June 1984).
To help determine the cause(s) of aesthetic or cosmetic effects from your drinking water, contact your local drinking water system. Additional guidance for household well owners is available at http://water.epa.gov/drink/info/well/index.cfm. General information on nuisance chemicals is available at http://water.epa.gov/drink/contaminants/secondarystandards.cfm .