STOCKTON (CBS13) — Stockton is warning several homeowners on the far north side of the city that their water may be contaminated.

The city found a higher chemical level in two wells, which may be caused by the drought.

Affected Stockton homeowners found a letter in their mailbox from the city saying tests at two of its wells on Oct. 14 found a chemical compound at levels higher than federal drinking water standards.

Long-term exposure to trihalomethane is linked to cancer, kidney, liver and central nervous system problems. The chemical is made when disinfectant chlorine combines with organic matter in water.

Residents were concerned how long it took them to be notified, as homeowners say the letters only arrived this week.

Stockton spokeswoman Connie Cochran says the letters were sent in November.

“They may not have opened them with the holiday mail, but we sent them out in November, so we have 30 days to notify,” she said.

She says there’s not an immediate risk, but homeowners are encouraged to call city hall with any questions.

“It’s actually not dangerous unless it were to occur over a number of years,” she said.

The city says water conservation efforts may have contributed to the problem. With fewer people using water, the chlorine and organic matter were allowed to sit and concentrate.

“We’re pulling in water from different sources. And the rain will help. It gets more water flowing through the system,” Cochran said.

The water will be tested again at the end of the month as part of a normal quarterly test and results could take several weeks to arrive.