The average bill for Wareham water users is going up, but high levels of two minerals that cause discoloration and health problems is coming down.

Voters at the Wareham Fire District Annual Meeting approved Monday funding a $12.5 million water treatment plant to address high amounts of iron and manganese in the drinking water supply.

Water officials said the problem of iron, which causes tap water to become a rusty color, is mostly cosmetic. However, it does generate a large amount of complaints.

High levels of manganese, on the other hand, is known to cause health issues, including neurological problems. The manganese issue prompted a warning from the Massachusetts Department of Environmental Protection to the district – either bring those levels down or face state intervention.

“The regulators have told us if we don’t act, they will act. They will dictate what we do, how we do it and how much we’re going to spend,” said Wareham Water District Superintendent Andrew Reid.

And by a vote of 99 to 26, annual meeting participants heeded Reid’s advice, but not before some vigorous protest.

“We don’t need this plant. I know you think we do…but you’re not paying the bill, we are,” resident John Assad told Reid. “We’re struggling with taxes and every kind of increase you can think of.”

Reid said approving the plant will increase the average water bill, which is between $250 and $300 bi-annually, by approximately $72.

In Wareham, water bills are based on usage. In a bid to spread the cost of the plant evenly, resident Ed Pacewicz introduced a measure that would have charged all water customers equally.

“We’re going to pay two to three times more for a plant than a seasonal person would. I don’t think that’s fair,” said Pacewicz referring to year round residents.

Pacewicz’s measure failed. Several voters said it was unfair to those who use a small amount of water, such as the elderly and small families, compared to high-volume commercial users.

The new plant will be funded with a low interest loan from the state, to be paid back over 20 years. According to the district’s consulting engineering firm, the plant will add $260,000 to the annual operating budget. Reid said future rate increases may be required to cover the cost. No new staff will be needed to operate the plant, Reid noted.