By John — Desalination News
Maui County is exploring whether desalination should become part of South Maui’s water supply after officials warned that the region’s main water system is edging close to its limits. At a community meeting in Kīhei this month, the Department of Water Supply said the Central-South Maui system delivered 26,795 million gallons a day at peak production last year against a rated capacity of 26,810 million gallons a day — leaving almost no headroom during the dry season.
Eva Blumenstein, the department’s planning program manager, told residents the area’s water demand is projected to grow by 6 million to 10 million gallons a day by 2040 as the county plans further development. Much of that growth is concentrated in South Maui’s drier watersheds, which have traditionally depended on water piped in from wetter parts of the island — an arrangement officials say is becoming less reliable as rainfall grows more erratic and Upcountry supplies come under competing demands.
The proposal on the table, drawn from a 2024 feasibility study by engineering consultant Brown and Caldwell, would build a $53 million brackish-water desalination plant in Kīhei using reverse osmosis and solar power, drawing from the nearby Kamaʻole aquifer. Brackish groundwater desalination is generally less energy-intensive than treating seawater directly, though the study found it would also yield less total freshwater, since output is capped by how much brackish water the aquifer can supply. The plant would start at half a million gallons a day and could scale to 2 million gallons a day. Brown and Caldwell identified three further potential sites elsewhere on Maui, ranging from $37 million to $80 million, including a saltwater plant in Lahaina.
Community reaction was cautious rather than hostile. Attendees generally didn’t reject the idea outright but pushed the department to exhaust conservation and water-reuse options first, and raised pointed questions about disposing of the leftover brine — a concern that has stalled or reshaped desalination proposals in other jurisdictions over environmental objections. The feasibility study recommends injecting the brine deep underground through injection wells, below the boundary separating drinking-water aquifers from the rest, with an engineer from Brown and Caldwell telling residents the plan requires “at least a 50-year path” before the brine would reach the ocean — an answer that left some in the room unsatisfied given Maui’s 2024 legal dispute over similar injection-well wastewater disposal.
County officials stressed that watershed restoration remains the department’s first priority and that desalination would supplement, not replace, that work. Council member Tom Cook, who chairs the Water and Infrastructure Committee, pointed to roughly 3 million gallons a day of recycled wastewater that could be redirected to irrigation to free up potable supply, though the pipes and tanks needed to move that water aren’t yet built. Other residents highlighted aging infrastructure — Maui maintains around 2,000 miles of water mains — and a water conservation ordinance signed by Mayor Richard Bissen in March as measures that could reduce how much new source water the county ultimately needs.
The county is weighing whether to apply for federal planning and design funding from the U.S. Bureau of Reclamation, but officials were careful to frame that step as exploratory. “It would not represent a decision to move forward with construction,” said James “Kimo” Landgraf, the water department’s deputy director. Maui would not be the first Hawaiian county to add desalination capacity — on Oʻahu, the Kalaeloa Seawater Desalination Facility is already moving forward, with an initial 1.7 million gallons a day planned for the ʻEwa area. A second South Maui community feedback session followed the Kīhei meeting in Lahaina.
(Source: Honolulu Civil Beat)