Starting January 1, 2026, Maui County's Department of Water Supply (DWS) will change how it projects water demand and
sizes water meters. This shift, mandated by Ordinance 5759, moves away from the Hunter Curve Method, which estimated
demand based on the number of plumbing fixtures in a building. The new system focuses on daily water usage.
The new method will apply to all building permit applications and requests for new or increased water use.
This updated approach, a type of water demand equivalent method, uses a unit called the Equivalent Single Dwelling (ESD)
to represent daily water demand. Daily water consumption will be estimated based on typical living patterns, considering
the number of bedrooms and bathrooms in a home. Any room that could reasonably be used for sleeping will be counted as a
bedroom. Each service will also be allocated an additional 0.5 ESD to account for outdoor water use, in addition to the
total ESDs associated with the service.
DWS developed a daily water usage model based on local meter data, per-capita usage, and national averages. This model
considers various bedroom and bathroom combinations and accounts for common household activities like dishwashing,
laundry, bathing, and general consumption. From this analysis, the department has set a fixed daily usage unit of 300
gallons per day for one ESD, based on a four-bed, two-bath home.
While the new method offers a more precise measurement of water demand, potentially revealing additional capacity under
the 300 gallons per day per ESD standard, it's important to note that it does not increase Maui's total water supply.
However, this approach enables DWS to plan and manage water resources more effectively while addressing the island’s
existing water challenges.
According to DWS Director John Stufflebean, this new methodology will allow for a more accurate measurement of water
demand. This ensures that properties are appropriately sized for safe and reliable water service. He added that it
supports Maui’s long-term water management goals, simplifies the process, and reinforces the department's commitment to
providing reliable service to the community.
To streamline the process for single-family residences, DWS has established standard meter capacities:
* 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 projects will use the same bedroom-and-bathroom methodology as single-family homes, with separate estimates
for outdoor water use. However, because water-use patterns differ from single-family homes, meter sizing relies on
modeling using the International Association of Plumbing and Mechanical Officials (IAPMO) Water Demand Calculator (WDC)
to reflect these unique patterns. DWS used models of various multifamily projects with different unit counts to develop
a sizing curve, which informs the standard meter table:
* 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 can either use the standard table or submit custom WDC calculations for meter sizing.
**Non-Residential Properties**
For non-residential properties, water demand will be determined through custom calculations prepared and signed by a
licensed professional. Developers must provide estimates for indoor water use and landscape irrigation, including plant
types, the area covered by each type, and anticipated daily or monthly water use. The EPA WaterSense Water Budget
Calculator can be used to assist with outdoor water estimates. DWS will convert all information into ESDs for permitting
and meter sizing. Custom calculations will also determine the meter issued and any associated storage and transmission
### Implementation Details
Existing multifamily and non-residential meters will maintain 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 help 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 by December 31, 2025, will still be processed under the current fixture-based method. The new
unit demand methodology will apply to applications submitted on or after January 1, 2026. It is important to note that
additional fixtures or ESDs will not be available for purchase under the new rules.
For further information, contact the DWS Engineering Division at 808-270-7835, option 5.