San Diego public utility workers began testing water for lead at San Diego Unified schools this week. It’s been widely reported a therapy dog at a school in Southcrest sniffed out the potential lead problem. But a district spokesman says the dog actually led custodians to discover another contaminant — one the city water tests won’t detect. Custodians at Emerson-Bandini Elementary School discovered old PVC pipes were leaching vinyl chloride into the drinking water after the dog refused to drink from its bowl, said spokesman Andrew Sharp.