How Greywater Can Be Reused

What Is Greywater?

Greywater is wastewater from household sources excluding toilets. It comes from baths, showers, washbasins, washing machines, and kitchen sinks. Water from toilets is called blackwater and requires more extensive treatment.

Greywater makes up 50–80% of household wastewater. Reusing it can reduce a household’s freshwater consumption by 30–50%.

Types of greywater:

Source	Quality	Contaminants
Bathroom (shower, bath)	Best	Soap, shampoo, skin cells, hair
Washbasin	Good	Soap, toothpaste, cosmetics
Washing machine (laundry)	Moderate	Detergent, fabric softener, lint, dirt
Kitchen sink	Poorest	Food scraps, oil, grease, detergents

Kitchen greywater has the highest organic load and is more challenging to treat. Many home systems exclude kitchen greywater or treat it separately.

Treatment Levels

Simple (low-tech): Screening + settling. Removes solids. Water suitable for subsurface irrigation of ornamental plants.

Moderate: Screening + settling + bio-filtration (sand or gravel filter). Suitable for garden irrigation and toilet flushing.

Advanced: Screening + settling + bio-filtration + disinfection (UV, chlorine, or ozone). Suitable for laundry, car washing, and surface irrigation.

Home Greywater Systems

1. Direct diversion (simple)

Greywater is diverted directly from the washing machine or shower to the garden through a 3-way valve. A simple filter removes lint and hair. Water must be used within 24 hours (before it turns septic).

Cost: ₹2,000–₹5,000 Best for: Garden irrigation with low-maintenance plants

2. Branched drain system

Greywater is distributed to multiple points in the garden through a network of pipes with no treatment. Requires careful design to avoid pooling.

Cost: ₹5,000–₹15,000 Best for: Established gardens in single-family homes

3. Treatment system (with tank and filter)

Greywater is collected in a tank, passed through a sand/gravel filter, and stored for later use. May include a pump for toilet flushing.

Cost: ₹25,000–₹80,000 Best for: Homes wanting to use greywater for toilet flushing and garden irrigation

4. Community system

Apartment complexes can install centralized greywater treatment systems. Treated water is used for landscape irrigation, car washing, and toilet flushing in common areas.

Cost: ₹5–15 lakhs for a 50-flat building Best for: Apartment communities

What Greywater Can Be Used For

• Garden irrigation: Best use. Subsurface irrigation is recommended (avoids human contact and odour)
• Toilet flushing: Requires treatment and storage. Can reduce water consumption by 25–30%
• Car washing: With moderate treatment
• Floor washing: With treatment and disinfection
• NOT for drinking, cooking, bathing, or swimming pools

What Soaps and Products to Use

Conventional cleaning products contain salts, boron, and chemicals harmful to plants. For greywater reuse:

• Use liquid soaps instead of bar soaps (bar soaps create soap scum that clogs pipes)
• Avoid sodium-based detergents — use potassium-based or greywater-friendly detergents
• Use low-phosphorus, low-salt, biodegradable products
• Avoid bleach, fabric softener, and boron-based products
• Look for products labelled “greywater safe”

Indian Examples

Greywater reuse in India is growing, especially in water-scarce regions:

• CSE, Delhi: The Centre for Science and Environment has installed greywater systems in its Delhi campus, treating and reusing water for gardening
• Mysore City Corporation: Implemented greywater treatment in municipal buildings for landscape irrigation
• Gurgaon apartment complexes: Several high-end apartments have centralized greywater systems for landscaping
• Rajasthan villages: Greywater is traditionally used for kitchen garden irrigation in water-scarce areas

Regulations

In India, the National Building Code (2016) encourages greywater reuse but does not mandate it for residential buildings. Some states and cities are introducing requirements:

• Bengaluru: BWSSB mandates greywater treatment and reuse for buildings above 20,000 sq ft
• Pune: New buildings above 5,000 sq m must have wastewater treatment and reuse systems
• Chennai: CMWSSB promotes greywater reuse through guidelines and subsidies

Key Takeaways

• Greywater is household wastewater from baths, sinks, and laundry (not toilets)
• Reusing greywater can reduce freshwater consumption by 30–50%
• Simple diversion to garden is cheap (₹2,000–₹5,000); treatment systems for toilet flushing cost ₹25,000+
• Use greywater-friendly, low-salt, biodegradable cleaning products
• Kitchen greywater is harder to treat — many systems exclude it