Here’s something to think about as we approach this weekend’s unofficial start of summer. Chlorine is added to pool water to help kill microbes that can cause disease. But when it mixes with uric acid, found in high concentrations in urine, it can form dangerous compounds, including trichloramine, which has been associated with lung problems, and cyanogen chloride, which can have adverse effects on the lungs, heart and central nervous system. Is there enough in your pool to harm you? The real question is: Why find out the hard way?