What is greywater?

Greywater is wastewater from:

  • Washing Machines

  • Showers

  • Baths

  • Spa Baths

  • Wash Basins

  • Laundry Troughs

  • Kitchen Sinks

  • Dishwashers

 

WHY USE GREYWATER?

Greywater is a resource. Greywater can be reused on-site for garden and lawn irrigation. Untreated Greywater contains nutrients, such as nitrogen and phosphorus which benefit plant growth. Treated greywater can be used for toilet flushing and laundry use (cold-water washing machine only).

When we make the choice to substitute the use of drinking water for irrigation, it will not only reduce the demand on drinking water supplies, but also reduce the amount of wastewater discharged to the environment.

 

How much greywater are we talking?

According to the Australian Bureau of Statistics, the average Australian household is 2.5 people. If we work with a three person household for round numbers, and calculate their water usage based upon average figures through AAA water saving devices and AAAA water saving appliances, if we then offset those conservative figures with a set of daily/weekly projected interactions, we can quickly determine an average greywater figure for the average household.

  • Shower: If each person has 1 x 7.5min shower per day through AAA (7.5 l/pm) water saving shower head = 1,181.25 litres per week.

  • Bath: If each person has 1 x 96litre bath per week = 288 litres per week.

  • Clothes Washing: 3 x 40L washing machine through a AAAA water saving front loading washing machine = 120 litres per week.

  • Kitchen: For the week, if their vegetables were rinsed in a shallow sink of water using a AAA water saving kitchen tap, if the dishes were rinsed before using their dishwasher and they only ran the dishwasher when it is full = 473 litres per week.

  • Basin: If each person used 100ml of water to brush their teeth twice a day. And used 250ml of water to wash their hands 3 times a day = 4.95 litres per week.

Based upon these figures, the total average weekly usage for a 3 Person Household using AAA water saving devices and AAAA water saving appliances is:

  • 2,067.2 litres of greywater per week.

  • 8,268.8 litres of greywater per month.

  • 99,225.6 litres of greywater per year.

To provide a visual on the average yearly quantity of greywater produced by a 3 person household, think of a rain water tank which is 2 meters high by 8 meters in diameter. The tank would be larger if non-water saving measures and devices were used.

 
 
100,000 Litre Water Tank. This tank’s capacity would match the average yearly quantity of water required for greywater fixtures to function in a 3 person household.

100,000 Litre Water Tank. This tank’s capacity would match the average yearly quantity of water required for greywater fixtures to function in a 3 person household.

 
 

GreyWater Systems Overview

When it comes to household Greywater Systems, there are two types.

  1. Greywater Treatment Systems

  2. Greywater Diversion Systems

 

Greywater treatment Systems

Greywater Recycling Systems recycle greywater from the shower, bath, basins, washing machine, laundry trough and kitchen (also called sullage). Greywater Recycling Systems are classed by the effluent standard they produce. There are three Greywater Effluent Standards. Greywater Treatment units must be certified against Australian Standard 1546.1 and require ongoing maintenance and servicing by an accredited service agent.

  1. Secondary Greywater Effluent Standard 20/30

  2. Secondary Greywater Effluent Standard 20/30/10

  3. Advanced Secondary Greywater Effluent Standard 10/10/10 

 

What do the numbers mean?

Each of the numbers relate to a Universal Measure of water quality.

The first number relates to Biochemical Oxygen Demand (BOD). The BOD is the amount of oxygen consumed by chemical processes and micro-organisms to break down organic matter in water over a 5-day period. BOD is measured in milligrams per litre (mg/L).

The second number relates to Total suspended solids (TSS). The TSS is the dry-weight of suspended particles, that are not dissolved, in a sample of water that can be trapped by a filter that is analysed using a filtration apparatus. TSS is measured in milligrams per litre (mg/L).

The third number (if present) relates to Escherichia coli (E. coli). E.coli is a species of bacteria in the faecal coliform group found in large numbers in the intestines of animals and humans. Its presence in freshwater indicates recent faecal contamination. E. coli is measured in ‘colony-forming units’ per 100 mL of water (cfu).

A Greywater Effluent Standard of 20/30/10 means the recycled greywater holds:

  • A BOD of 20 milligrams per litre.

  • A TSS of 30 milligrams per litre.

  • And an E.coli reduction of 10 colony-forming units per 100 ml.

 

Greywater Diversion Systems 

Greywater Diversion Systems are designed for immediate greywater reuse. There are a number of Greywater Diversion Systems which are available for purchase which are Watermarked and approved for use. They re-use untreated greywater from the shower, bath, basins, washing machine and laundry trough. Kitchen greywater can also be used in a Greywater Diversion System, providing the kitchen greywater runs though a Grease Trap prior to entering the Greywater Diversion System. Raw kitchen wastewater which contains fats, oils and grease (FOG) should not be diverted to gardens because the FOG can reduce the availability of air to plants and harm micro-organisms.

Untreated greywater can be reused temporarily providing the Greywater Diversion System is also connected to an approved on-site wastewater treatment system or municipal sewer for times of overflow or when redirection is required in wetter months.

 

GREYWATER reuse ADVANTAGES

Use fewer fresh water resources.

Irrigate your garden with reused water.

Reducing the amount of wastewater discharged to the ocean or rivers.

Reduce water bills.

A healthier garden, especially during drought
periods.

GREYWATER reuse DISADVANTAGES

Initial setup costs for greywater system and plumbing requirements.

Ongoing maintenance and system owner commitment.

The potential for pollution, and adverse health and environmental effects when greywater is not reused correctly.