Two drinking water samples taken Sept. 15 by the Scotts Valley Water District tested positive for coliform bacteria, an indicator that there could be more harmful bacteria in the water, though later tests suggested an error might have caused the positive readings.

As soon as the bacteria turned up during routine testing, the district took six more samples at three places along the water source. All six turned up negative, which points to some kind of sampling error that resulted in the two positive tests, operations manager Bill O’Brian said.

“It can be a piece of spider web, improper sampling or anything that gets in there,” O’Brian said. “The fact is we don’t know (what caused it).”

Generally, coliform bacteria are not harmful, O’Brian said. Coliform bacteria are naturally found in the environment, but when detected, they are used as an indicator that other, more harmful bacteria, such as fecal coliform or E. coli, might be present.

In this case, no harmful bacteria were found.

The positive results appeared in two of 15 samples the district collected and sent to an independent lab in the month of September. When two or more positive samples appear, California Department of Health regulations say the district must notify its customers.

“When you’re doing this many samples, these things do happen,” O’Brian said.