Tap water has far too many contaminants to be used in laboratories or for scientific purposes.
Impurities, elements and compounds in amounts as small as one part per trillion, can influence results in many research experiments. Heavy metals and dissolved organics, commonly found in tap water, are particularly damaging to life science research. The water must especially be free of any elements that are being measured. Because water purity is so important, several professional organizations have established water quality standards. Contaminant is any substances you do not want in your water.