Traces of antibiotics, estrogen, and antidepressants have been found in Canada’s water system, according to Canadian health officials. They promised yesterday to develop regulations requiring drug manufacturers to assess how their products would affect the environment. So far, the substances have been found in sewage effluent; the officials said drinking water would be tested shortly. John Carey of the national Water Research Institute said elevated estrogen levels in fresh water, likely from birth-control pills, have already affected the ability of young salmon to adapt to salt water.