Council reviews secondary irrigation master plan aimed at easing culinary water demand

Washington City staff and outside consultants presented a multi‑phase secondary irrigation master plan to the City Council on Jan. 8, 2025, outlining options to shift outdoor irrigation off culinary (drinking) water and onto pressurized secondary supplies.

The plan, presented by Lester Dalton, assistant public works director, and Delos Hammond, principal engineer with Alliance Consulting, inventories the city’s “paper” water rights and measured “wet” water, maps 14 pressure zones keyed to topography, and models three buildout scenarios: 1) energizing existing dry irrigation lines already installed in subdivisions (about 27% of the city), 2) adding irrigation for developable land, and 3) adding service to existing homes now on culinary water. The consultants said the city already has significant dry infrastructure that could be tapped to reduce culinary demand.

Why it matters: Council members and staff stressed that reducing outdoor use of culinary water is a priority for the city and region. Consultants told the council their analysis shows outdoor irrigation accounts for roughly two‑thirds of average household water use in Washington City, and that bringing a portion of that demand onto a secondary system could meaningfully extend culinary supplies.

Key points from the presentation included: consultants identified roughly 2,000 gallons per minute of papered irrigation water rights and about 948 gpm of measured wet water available today; to “wet” the existing dry lines (scenario 1) the city would need about 2,359 gpm and measured supplies fall short by several hundred gpm; the team proposed storage locations at higher elevations (Salente/Green Springs) to make water available across zones; and they recommended staged pilot projects (meter installations plus transmission and storage builds) rather than a single large bond.

Consultants emphasized water‑quality constraints for certain sources. Canal diversions from the Virgin River vary widely by season — high quality in spring runoff, lower quality with higher salts and silts during low‑flow months — and some well sources south of the river are brackish and corrosive without treatment. The study proposes settling ponds and blending strategies (for example, collecting diversion water and settling silt before blending with higher quality supplies) and identifies Warner Valley Lake and a centralized “Kirkland Pond” as strategic storage/collection sites.

Council members pressed technical and policy details: several asked whether water rights north and south of the river could be commingled (consultants said commingling is possible but requires detailed metering and legal review), how much of the city is already plumbed for pressurized irrigation (about 27% of lots have dry irrigation lines in place), and whether the city could leverage conservancy district impact‑fee rebates to fund construction in early phases (consultants said similar rebates have been used by other jurisdictions and could help). Staff and the consultants recommended starting with lower‑cost, high‑meter, high‑coverage projects (examples included Brio/Salente areas) to maximize number of accounts served per gallon of source water.

Council direction and next steps: Council discussed the need for follow‑up coordination with the Washington County Conservancy District and other regional partners and asked staff to return the plan to the regular meeting on Jan. 22 for formal consideration. Mayor and staff framed next steps as: (1) continue technical refinements and legal review of water‑right constraints, (2) meet with the Conservancy District to explore impact‑fee participation and storage options (Warner Valley Lake was cited as a regional storage alternative), and (3) return to council with an adoption agenda item and recommended short‑term pilot projects.

Deliberative context: Consultants and staff repeatedly described the plan as a “living” document and a phased roadmap rather than a single final buildout; they also urged caution about overfocusing on headline costs and recommended a step‑by‑step approach to capture “low‑hanging fruit” first.

For residents: the plan, if adopted, would not immediately change household water service. The phased approach seeks to add pressurized secondary service where feasible, install meters and enable billing, and protect culinary supplies; technical and legal constraints (including the State Engineer’s water‑right requirements and seasonal quality variations of canal waters) will determine timing and scale of changes.