Researchers suggest that Californians should boil or filter tap water, or use reliable bottled water. Based on a study of 5,000 pregnant women there just published in the journal Epidemiology, pregnant women who drink a lot of tap water could be at increased risk for miscarriage if the water contained high levels of chlorine by-products called tri-halo-methanes. Dr. Shanna (Shawn-ah) Swan co-authored the study. From her office at the California Department of Health Services in Emeryville, California she spoke with Steve Curwood. Swan says women who consume more than 5 -eight ounce glasses of tap water a day had the highest risk of miscarriage.