Water Rules of Thumb

Rule #1: As housing density increases, total water use per acre increases slightly, but water use per home drops substantially.

Single-family homes on larger lots use more of their water outdoors for landscaping, while townhomes and apartments generally have lower outdoor use.

• Per Acre → System impact (water supply, depletion, land use, Great Salt Lake)
• Per Home → Household efficiency (bills, conservation, fixtures, behavior)

Rule #2: Indoor water is mostly borrowed. Outdoor water is mostly spent.

An average single-family home in Utah uses approximately a third of its water indoors and the rest outdoors, primarily for landscaping. Most indoor use returns to sewer systems, where it’s treated and returned to streams and rivers. In some cases, this water can even be treated to a higher standard for additional human use. In the Great Salt Lake Basin, it provides much-needed flows to help maintain lake levels. 

Approximately 91 percent of outdoor use is consumed (also known as depletion), primarily through evaporation. The other nine percent eventually returns to streams and rivers through runoff, groundwater, and precipitation. Note on precipitation: most evaporative moisture is carried eastward out of the local water cycle by prevailing winds. 

Rule #3: As density increases, the share and total amount of return flows increase, while consumptive use typically declines.

Large-lot single-family housing tends to consume more water for landscaping irrigation, while townhomes and apartments/condos generate more return flows.

Rule #4: Water-wise landscaping can reduce outdoor water use and evaporative losses by up to two-thirds.

This is especially impactful for large-lot homes, where most residential water is typically used outdoors. Local programs such as Localscapes can provide information about designing yards that are beautiful, comfortable, and use less water. They may even provide rebates for waterwise landscaping!

Rule #5: Converting irrigated agricultural land to typical residential development often results in similar or somewhat lower total water use. Housing’s consumptive use is usually lower than agriculture, and return flows for higher density housing may be significantly higher than for agriculture.

In some cases, very large lot single-family homes may have higher consumptive use than agriculture.

On average, Utah’s common cool-season turf crops like alfalfa and pasture consume 70% of total water applied when irrigated with sprinklers (the irrigation method used in this assessment). By comparison, when using flood irrigation, about 50% of the total water applied is consumed by the crop, meaning total use is higher.