The Babylon Town Board has approved a $399,725 contract for design of a controversial drinking-water system on Oak Beach.

The cost from Melville-based H2M engineering firm fell in the middle range of three proposals evaluated by town officials, but it was chosen over a lower-cost option in part because of the firm’s experience in the field, town spokesman Kevin Bonner said.

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H2M has designed water systems for other beach communities including Ocean Beach and Long Beach, as well as systems Jones Beach, Captree and Robert Moses state parks.

The Oak Beach system is to include pipes and a centralized treatment facility for about 50 homes on the barrier beach.

Suffolk County health officials warned last year that the current patchwork of water pressurization and treatment at some Oak Beach houses is vulnerable to contamination, but some residents who now use private well water said a new system is not needed and is too expensive.

A portion of the cost, which town officials estimate $3 million, will be paid by those residents in the form of higher water bills. Yearly water bills could rise to $1,500, about five times what many now pay.