Assessing the Spatial Pattern of Water Use in the Tucson Water Service Area

1. Assessing the Spatial Pattern of Water Use in the Tucson Water Service Area Akitsu Kimoto and Evan Canfield: Pima County Regional Flood Control Tom Arnold: Tucson Water

2. Background • City of Tucson/Pima County Water Study • Joint Effort for Sustainable Water Resource Planning • Core Elements: Water Supply, Demand Management, Comprehensive Integrated Planning, Respect for Environment • Understanding Water Use Patterns is basic to address Demand Management, so the study had three focus areas: • Construction Pattern Changes and Water Use at a Parcel Scale • Per-Household Water Use Study • Per-Capita Water Use Study • Spatial Pattern of Water Use at a Subdivision Scale • Subdivision Water Use Study

3. Outline • Objective: Assess Water Use at a Subdivision Scale within Tucson Water Service Area. • We evaluated…. • Spatial patterns of subdivision water use • Spatial pattern of household size • Property value, area and subdivision water use • Variability of water use within an individual subdivision.

4. Data Used • Spatial Datasets (Pima County GIS library) • Parcel data • Subdivision data • Tucson Water Service Area boundary • Census Block 2010 data • Tabular Data • MAS 2011 (Pima County Assessor’s Office data) • Monthly water use data from 2009 and 2010 (Tucson Water) • Parsed Study Dataset • Removed parcels with a month of no water use • Used parcels with homes built before 2008 (“normal” level of water demand established) • Used subdivisions consisting of 100% single family residences (i.e. no multi-family residences) • Final dataset includes~ 70,000 residential customers in 1,200 subdivisions

5. Average Household Size (Number of People living in a House – 2010 Census) Southern and Southwestern Tucson: Larger Household Size

6. Average Household Monthly Water Use at Subdivision Scale (1 Ccf = 748 gals) Foothills: High Water Use High Low Central and Southern Tucson: Lower Water Use

7. Average Per-Capita Daily Water Use in Subdivision (GPCD) Foothills: High Water Use High Southern and Southwestern Tucson: Lower Water Use Lower Per-Capita Water Use in Southern/Southwestern Tucson can be related to the Larger Household/Newer, More Efficient Homes Low

8. Average Property Value for Subdivision(USD) High Low

9. Property Area, Property Value and Water Use Water use increasing with both parcel area and property value Best Fit with Logarithmic Line; Level off with increasing parcel area Best Fit with Liner Line; Stronger Fit than Parcel Area

10. Variability of Water Use within a Subdivision Example: Newer Subdivision constructed since 2000 77% of Homes are within this range Mean: 5454 sq ft SD: 941 Similar Sized Homes

11. Water Use within a Subdivision

12. Findings of the Study • Household size: • Large: southern and southwestern Tucson (More People live in Newer and More Efficient Homes) • Average per-household water use: • High: Foothills (often over 20 Ccf [15,000 gal/mo]) • Low: Central, Southern and Southwestern Tucson, (often less than 7.5 Ccf [~6000 gal/mo]) • Average per-capita water use: • High: Foothills (up to 300 GPCD) • Low: Southern and Southwestern Tucson (sometimes less than 50 GPCD) • Water use increases with both parcel area and property value. • A stronger relationship between property value and water use. • High variability in water use within a subdivision, even if the subdivision is similar in parcel area and house size (~30 GPCD to 130 GPCD).

13. Questions, Contacts and Resources • Contacts • Aktisu Kimoto akitsu.kimoto@pima.gov • Evan Canfield evan.canfield@pima.gov • Tom Arnold tom.arnold@tucsonaz.gov • City of Tucson – Pima County Water Study • http://tucsonpimawaterstudy.com/ • Report to be posted in next week or two