A new study suggests that some tap water -- despite being filtered and treated with chlorine -- may still be able to cause gastrointestinal problems in children, 10% of the serious gastrointestinal illness case in children -- the ones bringing the kids into the hospital -- are attributable to the drinking water, said the researchers at the Harvard School of Public Health.

Up to one-third of gastrointestinal illness may be related to drinking water that meets current federal standards, according to the report. And those illnesses can have a substantial impact on the economy, costing $5.9 to 24.3 billion, according to one 1991 estimate, which included direct medical costs of treatment as well as indirect costs, such as lost productivity and leisure time.

Children are not the only ones at risk from such gastrointestinal illnesses. Adults with weakened immune systems are also at risk, including those with AIDS, cancer patients undergoing chemotherapy or radiation treatment, or the elderly.

Epidemiology (1997;8:615-620)

COMMENT: Yet more support that one should avoid tap water completely. It appears that the chlorine does not even kill all the bacteria that is supposed to. If you haven't already please invest in a good filter for your tap. PUR filters (reviewed in July Consumer Reports) appear to offer the best value. The counter top model sell for about $70 at Target or Wal-Mart and wind up costing about 5 cents a gallon. Far less expensive than bottled water. If you have a water softener though it will NOT filter out the salt. You will need to purchase a far more expensive reverse osmosis system with pre and post carbon filtration.