The West Maui water system is operating above its maximum reliable capacity, and additional water service cannot be processed without developing new water sources, according to an analysis released Monday by the Department of Water Supply.

The system, which serves customers from Napili to Lahaina, has a maximum production capacity of 7.17 million gallons per day. But when accounting for uncertainties such as mechanical failures, weather events and other outages, the department estimates the system’s maximum reliable capacity to be 4.26 MGD.

To determine the maximum reliable capacity, the department assumed the Mahinahina Water Treatment Plant and one Waipuka well were offline.

Before the Aug. 8, 2023, wildfire, the combined 12-month moving average production for West Maui sources was 5.50 MGD. However, current demand is 129.1% of the system’s maximum reliable capacity, the department said.

Projected population growth is expected to increase demand. Pre-wildfire population forecasts in the 2030 Maui Island Plan show an average annual increase of 2.13%. Assuming eventual repopulation of the burn zone and a continuation of those projections, demand is expected to grow to 5.73 MGD by 2027.

The analysis found other factors contributing to demand, such as about 117 connected meters that are currently inactive, with no recorded consumption. Based on usage from similar meter sizes, the department projects these could add about 0.10 MGD.

The Department of Hawaiian Homelands also holds a 200,000-gallon-per-day allocation for its Honokowai and Village of Leiali’i Phase I-B projects under a 2019 agreement. As reservations convert to actual usage, demand is forecast to reach 6.04 MGD by 2027, including inactive meters and the DHHL allocation.

That level of demand would be about 141.8% of maximum reliable capacity, according to the department.

Because projected demand exceeds the system’s reliable capacity, the department said new or additional water service in West Maui cannot currently be processed.

To increase supply, the county is constructing a new groundwater source, the Kahana Well, which is expected to produce about 0.96 MGD and come online in early 2026.

The well is intended to offset reduced inflow to the Mahinahina treatment plant caused by interim instream flow standards.

Since Mahinahina is assumed offline in the reliability scenario, the Kahana Well would add to the system’s dependable capacity. Once operational, it is expected to reduce the three-year demand projection from 141.8% to 115.7% of reliable capacity.