HOLLIS, N.H. (AP) – One in four private wells has too much arsenic in the water, according to a voluntary study of water quality.

Tests on 125 wells found that those in the southeast part of Hollis were most likely to have more arsenic than is considered safe by the federal Environmental Protection Agency.

Arsenic occurs naturally in gray granite, which is common in New Hampshire.

The state doesn’t require homeowners to test their water, but public health officials strongly encourage it. They say homeowners should test for bacteria every year and should get comprehensive tests for arsenic, uranium and other contaminants every three to five years.

Arsenic can cause bladder, lung and skin cancer when it is consumed over a long period of time.