Two Approaches to Water Conservation
Homeowners interested in reducing potable water use for irrigation typically consider two systems: greywater reuse (capturing household wastewater) and rainwater harvesting (collecting roof runoff). Both are valuable, but they work differently, have different legal frameworks, and are best suited to different climates and property types. This guide compares them directly.
Side-by-Side Comparison
| Factor | Greywater Reuse | Rainwater Harvesting |
|---|---|---|
| Water source | Laundry, shower, bath water from your household | Roof runoff collected in tanks |
| Volume predictability | Highly predictable — depends on household habits | Highly variable — depends on rainfall |
| Year-round availability | Yes — you do laundry regardless of season | No — dependent on rain events |
| Best climate | Any climate — works year-round in dry climates | Better in areas with some rain distribution year-round |
| Installation complexity | Low (L2L) to moderate (shower system) | Low (barrel) to high (cistern + pump system) |
| Permit requirements | Varies by state — often no permit for L2L | Varies by state — often simpler than greywater |
| Water quality | Contains soaps, detergents, skin oils — subsurface use only | Cleaner — can use for drip irrigation, some states allow vegetable irrigation |
| Storage required? | No (L2L systems use-immediately model) | Yes — tanks or cisterns required |
| Maintenance | Low (L2L) to moderate (shower with surge tank) | Low (barrels) to moderate (cistern with pump) |
| Typical DIY cost | $80–$200 (L2L) | $100–$500 (barrel systems) |
When Greywater Is the Better Choice
- Arid climates (AZ, TX, NM, CA desert regions): Rainfall is too infrequent to depend on rainwater harvesting for reliable irrigation. Greywater from laundry and showers provides a consistent, year-round supply.
- Urban lots with limited roof area: Small roofs can't capture enough rain to matter. A 1,000 sq ft roof in Phoenix capturing 7 inches of rain yields about 4,000 gallons per year — less than 1.5 months of L2L greywater from a typical household.
- When you need water in dry summer months: Greywater keeps flowing regardless of weather. Rainwater tanks run out during dry spells.
When Rainwater Harvesting Is the Better Choice
- Vegetable gardens: Rainwater can be used on edible crops; greywater generally cannot.
- Simple compliance: Rainwater is often easier to permit (or permit-free) than greywater in states with complex greywater rules.
- Wetter climates (Pacific Northwest, Southeast): High rainfall makes rainwater harvesting more productive. Texas and Oregon, for example, receive enough rain in winter that large cisterns can provide irrigation water through dry summer months.
Using Both Together
The best approach for many properties is a combined system — greywater for permanent landscape irrigation of trees and shrubs (consistent, year-round), and rainwater harvest for vegetable gardens and supplemental irrigation (captured when available, used when needed). The two systems use different water quality levels for different applications, and together they can reduce potable irrigation demand by 60–80% in favorable climates.
If you're new to water conservation systems, start with whichever is simpler to permit in your state. In Texas and Arizona, L2L greywater is the obvious first step — no permit, low cost. In Washington and Oregon, a simple 55-gallon rain barrel may be the easiest entry point while you navigate the county greywater permit process.