CHUALAR 02/C/08MAY98/MN/CG --- A farmworker trudges through feilds adjusting sprinkler heads just east of the central valley town of Chualar, Ca., where rising Nitrate levels in the water, most likely from farm runoff, have caused the drinking water to be deemed unsafe. (CHRONICLE PHOTO BY CARLOS AVILA GONZALEZ) ALSO RAN: 11/22/2000 Ran on: 09-18-2004
 Irrigated farm field in California&amp;apos;s Central Valley.
 Ran on: 08-27-2007
 A farmworker walks through a field, adjusting sprinkler heads as he goes, just east of Chualar, where rising nitrate levels in the water from farm runoff have caused the drinking water to be deemed unsafe. Photo: CARLOS AVILA GONZALEZ