Twin Falls residents will shell out $43 million over the next three years to treat and expand their drinking water, after the Twin Falls City Council selected one of three possible options Monday night.

Facing high arsenic levels and a growing city, the council chose to build a 7.5-million-gallon-per-day treatment facility to treat water from the city's south wells and the Low Line Canal, providing 31 mgd and satisfying city needs until 2024. The council made its decision after new data from its consulting firm, J-U-B Engineers, showed retrofitting an initial 4,000 homes to use pressurized irrigation water would be extremely disruptive and possibly costly to homeowners.

Converting existing sprinkler systems and installing the PI systems could cost between $700 and $3,000 per home, J-U-B representative Mark Olsen said, for a rough total of $6 million that would have to be covered by homeowners or the city.

Council members did not say which method would be used to fund the projects.

Many council members said they felt the system, while the cheapest to maintain over its lifespan, would require a portion of the city to pay for something that would benefit the whole. And several of them questioned how the city would choose who had to be retrofit and who wouldn't.

"I just don't see a retrofit as politically feasible," Councilman David E. Johnson said.

While discussing its decision, the council made it clear it was betting on the future. The option it chose included a phase of retrofitting before 2024, but several council members said they wanted to leave things open for the future. The city is actively seeking new sources of water, they said, and new technologies could open up better possibilities for future expansion.

Others mentioned better conservation measures as something to strive for, and Councilman Trip Craig suggested urging other cities to adopt the water conservation measures Twin Falls has.

The council also dismissed a third option, which would have built a $50.7 million, 10 mgd treatment plant and expanded it later for $15.4 million more.

City staff will now proceed to develop plans for the 7.5 mgd plant, to be constructed and operational by early 2011.

Nate Poppino can be reached at 735-3237 or npoppino@magicvalley.com.