Beginning Jan. 1, 2026, in accordance with Ordinance 5759 adopted by the Maui County Council, the County of Maui Department of Water Supply (DWS) will implement a new method for projecting water demand and sizing water meters that focuses on daily water usage instead of the Hunter Curve Method, which was based on the number of plumbing fixtures—such as toilets or showers—in a building. The new method will apply to building permit applications and applications for new or additional water use.

The new approach is a form of the water demand equivalent method, establishes a unit of daily water demand called the Equivalent Single Dwelling (ESD), and estimates daily water consumption based established patterns of human habitation correlating to the number of bedrooms and bathrooms in a home, counting any room that is, or could reasonably be, used for sleeping as a bedroom. In addition to the total ESDs associated with a service, each service will be allocated an additional 0.5 ESD to account for outdoor water use.

Analyzing empirical local meter data, per-capita usage and national per person daily use averages, DWS developed a model for daily water usage based on a range of bedroom and bathroom combinations accounting for typical household activities such as dishwashing, laundry, bathing and general human consumption. From this analysis, the department established a fixed daily usage unit of 300 gallons per day for one ESD, based on a four-bed, two-bath home.

The new method provides a more accurate way to measure water demand, which may show additional available capacity under the 300 gallons per day per ESD standard, but it does not increase the total water supply on Maui. This approach helps DWS plan and manage water resources more realistically while continuing to address the island’s ongoing water challenges.

“This new methodology allows DWS to more accurately measure water demand and ensure properties are appropriately sized for safe and reliable water service,” said DWS Director John Stufflebean. “It supports Maui’s long-term water management goals, helps make the process more straightforward, and reinforces our commitment to serving the community reliably.”

Single-Family Homes

For single-family residences, DWS has established standard meter capacities to simplify the process:

• 5/8-inch meter: up to 2.5 ESDs
• 3/4-inch meter: up to 3.5 ESDs
• 1-inch meter: up to 6 ESDs

Multi-Family Homes

Multi-family projects use the same bedroom-and-bathroom methodology as single-family homes, with outdoor water use estimated separately; however, because multifamily buildings have different water-use patterns than single-family homes, meter sizing is based on modeling using the International Association of Plumbing and Mechanical Officials (IAPMO) Water Demand Calculator (WDC), reflecting their unique water-use patterns. Models of different multifamily projects with varying unit counts were used to develop a sizing curve, which informs DWS’s standard meter table:

For multi-family residences, DWS has established standard meter capacities as:

• 1-inch meter: up to 16 ESD
• 1.5-inch meter: up to 60 ESD
• 2-inch meter: up to 120 ESDs
• 3-inch meter: up to 240 ESDs

Developers may use the standard table or submit custom WDC calculations for meter sizing.
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Non-Residential Properties

For non-residential properties, water demand is based on custom calculations prepared and signed by a licensed professional. Developers must provide indoor water-use estimates as well as landscape irrigation calculations, including plant types, the area covered by each type, and anticipated daily or monthly water use. Developers may use the EPA WaterSense Water Budget Calculator to assist with outdoor water estimates. DWS will convert all information into ESDs for permitting and meter sizing, and custom calculations also determine the meter issued along with any associated storage and transmission fees.

Implementation and Transition

Existing multifamily and non-residential meters retain ESD entitlements based on their current approved use or the FY2026 source fee equivalent of $2,316 per ESD, whichever is greater. DWS will not reduce existing entitlements or require reconciliation for customers whose entitlements exceed fees paid.

To assist with the application process, the updated ESD Methodology and a Materials Submission Checklist will be available at www.mauicounty.gov/214/Engineering-Division.

Applications submitted on or before Dec. 31, 2025, will continue under the current fixture-based method. Applications submitted on or after Jan. 1, 2026, will use the new unit demand methodology. Additional fixtures or ESDs will not be available for purchase under the new rules.

For more information, contact the DWS Engineering Division at (808) 270-7835, option 5.

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