The San Joaquin County Public Works Department expects the trouble to be cleared up sometime today. The department suspects there was a problem with the sample rather than the water supply, which was tested two days earlier with clean results, said a county worker who asked for anonymity because he was unauthorized to speak for the department.
The presence of E. coli or fecal matter in the sample prompted notices telling residents to boil water for a minute and let it cool before “drinking, making ice, brushing teeth, washing dishes and food preparation until further notice.”
The bacteria can cause serious illness and even death and poses higher risks for infants, young children, the elderly and people with weak immune systems.
New samples have already been collected and will be tested at an outside laboratory, the county worker said.
The bacteria can contaminate water following run-off after heavy rains; it can get into water if a pipe breaks; and sometimes can contaminate water if there’s a problem with a water treatment plant, residents were told.

Ya asked, "Where is the water treatment plant for the County?"
Thair ain't one. People in th county either use bottled water, have it hauled in an stored in a tank or have thair own water well. Generally they have thair own well.
Regardless, water treatment is on them.
Now fer sewage they either have holdin tanks that have ta be pumped an hauled away or, if th ground will percolate it, in ground septic tank systems that treat th water an release it inta th ground.
Now thair are some small communities that are not towns or cities that could share a communal well an septic system but thair ain't many of those an mostly th people livin out in th county each have thair own well an septic system.
Hope that answered yer question.
--------------------------
'The department suspects there was a problem with the sample rather than the water supply, which was tested two days earlier with clean results'