This document describes an experimental project to collect and filter gray water from shower and bathtub drains to reuse for flushing toilets and irrigation. Gray water is collected in recycled 55-gallon drums and filtered through a spun polypropylene mesh pre-filter and slow sand filter based on a design from CAWST, a non-profit providing water treatment. An Arduino controller is used to pump filtered water and drain stale gray water. The system cost around $950 and currently collects 40-70 gallons of gray water per day which will be tested for purity before use in toilets.

1. Collection of Residential
Shower and Bathtub
Gray Water for
Reuse to Flush Toilets
and for Irrigation
An Experimental Project
Kenneth Garges

2. Gray Water
• Collected from bathtub and shower drains.
• NOT potable.
• Quickly fouls if stored.
• Fresh gray water can be used for
subsurface irrigation but not sprayed.
• Not pure enough for toilets.

3. Filtering Gray Water
• Commercial systems are very expensive.
• Example: Flowtender price $3840 - $18,968

4. A New Simpler System
• Collection in recycled 55 gallon drums.
• Spun polypropylene mesh pre-filter.
• Slow sand (aka biosand) filter modeled
after Center for Affordable Water and
Sanitation Technology (CAWST), a non-profit
delivering water treatment systems
to developing countries.
• Pump controlled by Arduino to keep
storage brief by draining stale gray water.

9. Current Project Status
• Collection tank plumbed to shower drains
• Filtration tank completed, running for 20
days (CAWST recommends at least 30
before using filtered water)
• Filtered water storage tank completed but
not plumbed to building toilets
• Controller hardware finished
• Software still in progress

10. Cost and Benefit
• Total hardware cost ~$950.
• Mostly Home Depot, Granite Rock, eBay.
• Currently collecting 40-70 gallons/day.
• Purity of filtered water not yet tested but
looks promising.
• Similar to systems in developing countries.
• Current city regulations may need revision.