Approximately 60% of water that is consumed is converted to Greywater.
The term “Greywater” can be defined as untreated wastewater generated either directly or indirectly by human activities having no fecal contamination.
When this untreated wastewater is stored, even for short periods, the water often clouds and turns grey in colour. This is why it is called as greywater.
Greywater is also referred to as Sullage or foul water.
While greywater looks dirty, it can be used for several different applications before being completely discarded into the sewage system for treatment.
Sources of Greywater
By defination all greywater is waste water, but not all waste water is greywater. Some definitions include the water sourced from various kitchen appliances while the others don’t.
Some common sources of greywater are:
- Basins/Sinks
- Showers
- Washing Machines
- Kitchen Appliances
- Washing of cars
- Washing of homes/offices
The exact sources of greywater may vary according to countries and organizations.
Quality of Greywater
The quality of the greywater determines the applications for which it can be used effectively. Greywater is usually warm and contains different types of organic matter and some nutrients.
Here is a list of common sources of greywater.
| Source | Possible Contents |
| Washing Machine | Suspended Solids(dirt,lint), organic material, oil and grease, sodium, nitrates and phosphates (from detergent), bleach |
| Dishwashers | Organic Material, suspended solids (food particles),bacteria, detergent, oil, grease |
| Shower, washbasins | Bacteria, hair, organic material, suspended solids (skin, particles), oils, soap, shampoo, toothpaste |
| Kitchen Sinks | Bacteria, organic matter, suspended solids (food particles), fat, oils, grease, soap, detergent residue |
| Floor and other washing wastes | Dirt, soap, detergent, bacteria |
Typical Composition of Greywater
| Parameter | Unit | Range/Value |
| Suspended Solids | mg/L | 45-330 |
| Turbidity | NTU | 22-200 |
| BOD5 | mg/L | 90-290 |
| Nitrite | mg/L | <0.1-0.8 |
| Ammonia | mg/L | <0.1-25.4 |
| Total Kjeldahl Nitrogen | mg/L | 2.1-31.5 |
| Total Phosphorus | mg/L | 0.6-27.3 |
| Sulphate | mg/L | 7.9-110 |
| pH | – | 6.6-8.7 |
| Conductivity | mS/cm | 325-1140 |
| Sodium | mg/L | 29-230 |
Depending on how the greywater is managed, its contents and nutrients can prove to be beneficial to the various applications.
Quantity of Greywater
Greywater quantity keeps on varying based factors such as :
- Number of members in the household or offices
- Age distribution of members
- Lifestyle characteristics
- Water usage patterns
- Climatic and environmental conditions
It is estimated that greywater makes up approximately 60% of all wastewater. This means that 60% of all water that is consumed will be converted to greywater.
As identified by standard water requirements, an individual can consume approximately 135 lpd. Based on this, it would imply that an individual can generate approximately 81 L of greywater per day.
Greywater generated by an individual:
- Per day = 81 L
- Per Week = 567 L
- Per Month = 2,430 L
- Per Year = 29,565 L
Applications or Uses of Greywater
Greywater has varied applications as non-potable water depending on its source and composition. Though it is not impossible to use untreated greywater, treated greywater has more applications.
- Toilet Flushing
- Gardening, Irrigation or Landscaping
- Firefighting
- Heat Reclamation
- Industrial Use
- Car Washing
- Ornamental uses in fountains, artificial waterfalls
Significance of Greywater Reuse
Resusing of greywater enables the utilization of an on-site resource which would other wise be wasted. Greywater reuse helps in
- Conserving of fresh water or potable supplies
- Reusing of nutrients
- Groundwater recharging
- Reducing load on waste water treatment plants thus saving money spent by authorities
- Reducing water wastage
- Reducing energy consumption
Guidelines for Greywater Reuse
In order to reuse greywater effectively, the following objectives help establish the basic guidelines.
- Prevention of
- Public Health Risk
- Possible disease transmission arising from improper greywater reuse
- Ensuring the greywater systems do no pose any harm to the environment or native ecosystems
- Protection of
- Groundwater
- Surface Water
- Land and Vegetation
Working of the Greywater System
The working of the greywater system consists of four steps:
- Collection of Greywater
- Several methods can be employed to collect greywater from all its different sources. It is highly recommended to install proper plumbing in order to collect this greywater since it requires less maintenance and can transfer the collected greywater directly to its designated storage.
- Storage and Treatment
- Collected greywater is immediately stored. It is recommended that collected greywater be stored for less than 24 hours. In order to store this greywater for longer periods for various applications, it should be filtered to remove suspended solids and particles and then be treated with Chlorine or Iodine.
- Based on the application for which the greywater is going to be used, different treatment procedures may also be adopted.
- Use of Greywater
Methods to collect Greywater
In order to reuse greywater, it is imperative to collect the said greywater. The following methods can be adopted for the same:
- Manual Collection – To collect using bucket or jug by hand
- Simple Piping – To collect using plumbing connections and systems between source and storage tank or area of application
- Integrated Sewage and Piping – To collect using plumbing connections and systems between all sources and the collection tank with provisions for treating the greywater with chlorine or iodine for longer storage.
