Estimating Individual Customer and Utility-wide Residential Irrigation Demand in Southwest Florida

Abstract

Planning agencies often incorrectly assume that all residential customers irrigate the same amount. The objectives of this study were to 1) determine which customers were irrigating, 2) compare the irrigation use to an assumed value used by the Southwest Florida Water Management District (SWFWMD), and 3) estimate utility-wide irrigation use. Irrigation demand was calculated using monthly potable billing records and irrigation required was calculated using soil-water balances. The ratio of irrigation demand to irrigation required was used to statistically group customers, which resulted in 10% to 17% of customers, depending on utility, being identified as “irrigators.” Total annual irrigation demand of all customers combined and just the “irrigator” group was 26.2 billion and 8.6 billion gal, respectively. The calculated irrigation demand when considering all customers was 111 gal per account-day (gpad), whereas the calculated irrigation demand of only those customers identified as “irrigators” was 256 gpad. These results were below SWFWMD’s estimate of 300 gpad, indicating that their irrigation estimate is too high when considering all customers and may still be too high when considering only “irrigating” customers. The results of this study can be used to assist Florida utilities in estimating the irrigation demand of residential landscapes, which could improve their potable water demand predictions.