Greywater reuse: a practical, safe guide

Greywater is lightly used water from showers, baths, bathroom basins and washing machines. It is not the same as blackwater (toilet waste) or heavily contaminated kitchen water, and with simple precautions it can be a useful garden resource — particularly in drought conditions.

What greywater is (and isn't)

Greywater is the relatively clean wastewater produced by washing: showers, baths, bathroom hand basins and washing machines. It contains soap residues, skin cells and small amounts of bacteria, but it is far less contaminated than:

• Blackwater — toilet waste (urine, faeces). Never reuse this.
• Kitchen sink water — contains food particles, fats and often more bacteria than shower water. Best avoided or treated separately unless you use a dedicated system.
• Dishwasher water — very hot and high in detergent; not suitable for gardens.

How "grey" your greywater is depends heavily on what goes into it. A warm rinse from the shower is much cleaner than a load of heavily soiled nappies or a machine wash with bleach-based detergent.

Why reuse it?

Garden watering can account for a large portion of household water use, especially in summer. Replacing that with water you've already heated and paid for makes sense. It also takes pressure off local water supplies during dry spells — see our full guide to saving water at home for the bigger picture. In drought-prone regions, greywater reuse is an accepted and sometimes encouraged practice. In wet climates, the benefit is smaller but still real.

Simple, low-risk methods

The simplest approaches require no plumbing and no permits.

Shower warm-up water

While you wait for the shower to run hot, place a bucket or large bowl under the flow. That cold water is perfectly clean — no soap at all — and can go straight on the garden, into a watering can, or into the toilet cistern for flushing. Many households collect several litres a day this way.

Bath water

A bucket or a small hand pump (sold for this purpose) lets you transfer bath water to a watering can. Apply it to ornamental plants and lawns by pouring at the base of plants, not spraying it overhead. Use it the same day.

Washing machine diversion — simple hose method

Many washing machines have a flexible outlet hose. Some people temporarily redirect this into a bucket or outdoor drain while the machine runs, then use the collected water on the garden. This works, but watch the volume — a single wash can produce 50–100 litres. You need to be ready to use it quickly and ensure runoff doesn't reach drains, neighbours or waterways.

Safety rules and legal notes

Step-by-step: safe bucket greywater

1. Switch your products. Before you start, make sure your shampoo, body wash and laundry detergent are plant-safe and phosphate-free. This is the most important step.
2. Collect the water. Place a bucket in the shower to catch warm-up water, or use a hand pump to transfer bath water after bathing. A 10-litre bucket is a practical size.
3. Check what you collected. If it contains a lot of foam, bleach, hair dye, medications or cleaning products, discard it down the drain this time. Only use water that is lightly soapy.
4. Take it straight to the garden. Don't leave it sitting. Carry or pour it to ornamental plants, trees, shrubs or lawn within a couple of hours.
5. Apply to soil at the base of plants. Tip slowly so it soaks in rather than running off. Avoid puddles, which can attract insects and create odour.
6. Wash your hands. Treat greywater as you would any moderately dirty water.
7. Rest the same patch of soil periodically. Greywater can build up salts and alter soil pH over time. Alternate with rainwater or mains water, and occasionally water thoroughly to flush salts through.

Plumbed diverter and treatment systems

If you want to divert washing machine or bath water automatically without carrying buckets, there are two main options:

• Simple diverter valves — a manually operated valve installed on your washing machine or bath outlet that redirects water to an outdoor hose or holding point. Relatively inexpensive, but even these may require building consent in some areas.
• Treatment systems — larger installations that filter, disinfect and sometimes store greywater. These are more capable (can handle kitchen greywater, allow storage, may allow drip irrigation to food gardens) but they are more expensive and virtually always require professional installation, permits and compliance with local standards.

Get a qualified plumber or irrigation specialist involved for any permanent plumbed system. This is not a job for DIY unless you are qualified; incorrectly installed systems can back-contaminate your drinking supply or violate regulations.

What not to reuse

• Toilet water (blackwater) — never.
• Water from washing nappies, heavily soiled clothing or anything contaminated with faecal matter.
• Water containing bleach, strong disinfectants, hair dye, pharmaceutical products or boron-based products.
• Dishwasher water — hot, highly concentrated detergent, damaging to soil.
• Water from anyone in the household who is ill with a gastrointestinal infection.
• Greywater that has been sitting for more than a few hours.

Greywater checklist

• Switched to phosphate-free, plant-safe soap and detergent.
• Collecting shower warm-up water in a bucket daily.
• Using collected water within a few hours, never storing overnight.
• Applying to soil only — not spraying onto leaves or edible parts.
• Keeping children and pets away during application.
• Checked local regulations before considering any plumbed system.
• Alternating greywater with clean water to prevent salt build-up.