Xeriscape Water Savings Calculator
What this xeriscape water savings calculator does
This calculator estimates how much outdoor irrigation water (in gallons) and water-bill cost (in dollars) you could save in a typical year by replacing a conventional turf lawn with a lower-water xeriscape design. You enter your lawn size, how much you typically water, how long your watering season lasts, an estimated percent reduction after xeriscaping, and your water price per 1,000 gallons.
Inputs explained (and how to pick good values)
- Lawn area (sq ft): The portion you currently irrigate as turf. If you’re converting only part of the yard, use just that area.
- Watering depth per week (inches): The total depth applied across the lawn each week (from sprinklers), not rainfall. Common ranges are roughly 0.5–1.5 in/week depending on climate and season.
- Watering weeks per year: The number of weeks you irrigate in a typical year. Many locations have a distinct irrigation season (for example, 16–20 weeks in cooler climates, 26–35 in transitional climates, and 35–52 in warmer/arid climates).
- Water-use reduction with xeriscape (%): How much less irrigation the new landscape uses compared with turf. If you’re installing drought-tolerant plants, improving soil, mulching, and using drip irrigation, a 50–80% reduction is commonly cited. The default 70% is a reasonable “strong but plausible” estimate in many dry climates.
- Water cost per 1,000 gallons ($): Your utility’s price for water (and sometimes sewer) per 1,000 gallons. If your utility uses tiers, use your marginal (highest) tier for a better estimate of savings.
Formulas used
The key conversion is that 1 inch of water over 1 square foot equals about 0.623 gallons. Using that, annual lawn irrigation is estimated as:
- G = annual gallons used for irrigation
- A = lawn area (sq ft)
- D = watering depth per week (inches)
- W = watering weeks per year
Xeriscape gallons are estimated by applying your reduction percentage R:
- Gallons saved =
G × (R/100) - Xeriscape gallons =
G × (1 − R/100)
Cost savings use your price P per 1,000 gallons:
- Annual $ saved =
(Gallons saved / 1000) × P
How to interpret the results
- Annual gallons saved: The estimated reduction in irrigation water versus turf, based on your inputs. This is the easiest number to compare to drought goals or local conservation targets.
- Annual cost saved: A simple bill estimate based on your per‑1,000‑gallon price. If your city has tiered rates, your true savings may be higher or lower depending on which tier you’re avoiding.
- What the reduction % really means: A 70% reduction assumes the xeriscape is designed and maintained for low water use (right plant selection, mulch, efficient irrigation, correct scheduling). If you keep large irrigated ornamental areas, choose thirsty plants, or overwater, the realized reduction can be much smaller.
Worked example
Scenario: You have a 1,000 sq ft lawn. You water 1.0 inch/week for 26 weeks/year. You expect xeriscaping to cut irrigation by 70%. Water costs $4 per 1,000 gallons.
- Annual turf irrigation:
G = 1000 × 1.0 × 0.623 × 26 = 16,198 gallons - Gallons saved:
16,198 × 0.70 = 11,339 gallons - Annual $ saved:
(11,339 / 1000) × 4 ≈ $45.36
Over 10 years, that simple projection is about 113,390 gallons and $454 saved, before considering changes in water rates, climate, or the initial establishment watering phase.
Comparison table: how watering depth affects savings
The table below holds area (1,000 sq ft), season length (26 weeks), reduction (70%), and price ($4/1,000 gal) constant and varies only weekly watering depth.
| Weekly depth (in) | Traditional gallons/yr | Xeriscape gallons/yr | Gallons saved/yr | $ saved/yr |
|---|---|---|---|---|
| 0.5 | 8,099 | 2,430 | 5,669 | 22.68 |
| 1.0 | 16,198 | 4,859 | 11,339 | 45.36 |
| 1.5 | 24,297 | 7,289 | 17,008 | 68.03 |
Assumptions & limitations (read this for accuracy)
- Rainfall is not modeled. This assumes your irrigation schedule doesn’t change due to rain. In reality, effective rainfall can reduce irrigation needs significantly in some regions/seasons.
- Irrigation efficiency is simplified. Sprinkler distribution uniformity, runoff, wind drift, and overspray can change actual gallons used. Drip systems can be more efficient, but only when designed and maintained correctly.
- Soil type, slope, and sun exposure aren’t included. Sandy soils, steep slopes, and full-sun exposures often require different scheduling than clay soils or shaded yards.
- Plant establishment period. New xeriscapes may need extra watering in the first months/first season for establishment; long-run savings may be lower in year 1.
- Reduction percent is an estimate. “Xeriscape” can range from nearly zero irrigation (native, non‑turf) to moderately reduced irrigation (ornamentals on drip). Use a conservative reduction if you’re unsure.
- Water pricing can be complex. Many utilities use tiered rates, seasonal surcharges, fixed service fees, and sometimes sewer charges that don’t decrease with outdoor use. For best results, use the marginal water-only rate you expect to avoid.
- Local rules and restrictions vary. Watering-day restrictions, drought stages, and rebate programs can affect both watering weeks and financial outcomes.
FAQ
How many gallons is 1 inch of water on 1,000 sq ft?
About 623 gallons (because 1 inch × 1,000 sq ft × 0.623 ≈ 623 gallons).
Does xeriscape mean “no watering”?
Not necessarily. Many xeriscapes need little supplemental irrigation after establishment, but some designs (and many climates) still benefit from occasional deep watering.
What reduction percentage should I use?
If you’re unsure, try a range: 50% (conservative), 70% (common target), and 80% (aggressive/optimized). Compare the outputs to see how sensitive savings are to design quality and watering habits.