EMPIRICAL METHODS FOR ESTIMATING AND PROJECTING WATER USE IN THE SEACOAST REGION, SOUTHEASTERN NEW HAMPSHIRE

New methods were developed to estimate water use in the Seacoast region in southeastern New Hampshire for 2003 and project future water demand in 2017 and 2025 as part of a regional ground-water availability study. The methods focused on estimating 2003 water demand as the basis for determining withdrawal, delivery, consumptive use, release into sewers, return flow, and transfer by users at the census-block and town scales. Measurements of withdrawal and return flow, where available, were used to check the validity of the demand estimates.

Domestic water demand was estimated using a per capita water demand model that related metered deliveries to domestic users with census block and block-group data. The model was used to predict annual, summer, and winter per capita water-demand coefficients for each census block. Using data from the 2000 U.S. Census, significant predictors of domestic water demand include population per housing unit, median value of owner-occupied single family homes, median year of housing construction, population density, housing unit density, and proportion of housing units that are in urban areas. The mean annual domestic per capita water-demand coefficient in the Seacoast region was 75 gal/d; the coefficient increased to 91 gal/d during the summer and decreased to 65 gal/d during the winter. Domestic consumptive use was estimated as the difference between annual and winter domestic water demand. Estimates of commercial and industrial water demand were based on coefficients derived from reported use and metered deliveries. A relation was established between current commercial and industrial employee numbers and water demand. Projections of domestic, commercial, and industrial water demand in 2017 and 2025 were determined by using the housing and employee projections for those years developed through a privately-developed Transportation Demand Model and applying current domestic and non-domestic coefficients.

Domestic water demand is projected to increase by 54 percent from 19.0 Mgal/d to 28.7 Mgal/d from 2003 to 2025 based on projection of future population growth. Non-domestic (commercial, industrial, irrigation, and mining) water demand is projected to increase by 66 percent from 7.3 Mgal/d to 11.8 Mgal/d from 2003 to 2025.