What counts as greywater?

Greywater is wastewater from showers, bathtubs, bathroom sinks, and clothes washers. It does not include toilet waste (blackwater) or kitchen sink/dishwasher water, which contain food particles and pathogens that make treatment more complex.

Can I really irrigate with laundry water?

Yes. The simplest permitted greywater system — laundry-to-landscape — diverts washer discharge directly to mulched basins around trees and shrubs. Use plant-safe, low-sodium detergent. Avoid using it on edible parts of food crops.

How much greywater does a typical household produce?

A rule of thumb is 25–40 gallons per person per day for combined shower, sink, and laundry sources. Actual amounts depend heavily on shower duration and whether high-efficiency fixtures are installed.

How is irrigation coverage calculated?

The calculator uses a standard landscape irrigation depth of 1 inch per week (roughly 0.623 gallons per square foot per week). Your daily greywater volume is converted to weekly volume and divided by that rate to give irrigable square footage.

What permits do I need?

Requirements vary by jurisdiction. Many US states have adopted simplified greywater codes (California, Arizona, Texas, Oregon) that allow laundry-to-landscape systems with minimal permits. Always check with your local building or health department before installation.

Does greywater need to be treated before use?

Simple systems that direct water immediately to mulched soil rely on the soil as a biofilter and do not require chemical treatment. Storage-based systems that hold water more than 24 hours typically require treatment to prevent odor and pathogen buildup.

How much does a greywater reuse system cost?

A DIY laundry-to-landscape diverter system runs roughly $150–$400 in parts. Permitted branched-drain systems for showers and sinks typically cost $1,000–$3,000 installed, while filtered storage systems with pumps can run $4,000–$10,000 or more. Use the annual-savings output to estimate payback against the upfront cost.

Greywater Reuse Calculator

Name: Greywater Reuse Calculator
Availability: InStock
Author: Nham Vu

Estimate daily greywater output from showers, sinks, and laundry, then see how much irrigation area you can cover and how much potable water you can save.

Household Parameters

Number of People

Showers / Baths

Minutes per shower

Flow rate (gal/min)

Showers per person per day

Bathroom Sinks

Minutes per use

Flow rate (gal/min)

Uses per person per day

Laundry (Clothes Washer)

Loads per week

Gallons per load

Standard washer ~40 gal/load; HE front-load ~15–25 gal/load.

Water Rate ($ per 1,000 gal)

US average ~$3.50–$6.00/1,000 gal. Check your water bill.

Fill in your household details and click Calculate to see results.

Summary