One, the water isn't poisoned. Arsenic occurs naturally, and can be found in trace amounts in just about every metal product in existence. The SEATTLE schools had just put in new fixtures, and in some cases the water had been stagnant in the pipes for a while. They are looking at that as the probable cause. 10 years ago, the amounts found wouldn't have even been reported, because they are far below the amount you would have to consume to cause harm. The EPA recently lowered the amount of arsenic allowed in potable water from 50 to 10 PPB. (parts per Billion)