State health officials are telling many Mason City residents to find a new source of drinking water — and go to the doctor for blood tests. The warnings come after repeated checks on the south side of Mason City show high levels of arsenic in the water supply. State Toxicologist Dr. Charles Barton says there are grave health risks to those who have daily, long-term exposure to arsenic, such as cancer, hypertension, heart disease, kidney disease and spontaneous abortions.If a smoker is exposed to arsenic, their risk of contracting cancer doubles.State environmental specialist Jeff Vansteenburg says they don’t know why the arsenic is in the water, but they suspect it comes from glacial deposits. Vansteenburg recommends digging deeper wells as some deeper municipal wells don’t show arsenic.He says residents may be able to remove the arsenic with a water purification system.State officials met with Mason City residents last night to discuss the situation.