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Gray Water Treatment & Use : Some doubts!

We are building a 5-Story office building with two bathrooms on each floor. We want to recycle the Grey water from the sinks. There are no kitchens, or laundry facilities-the gray water is only from wash basins in restrooms.

My question is: can we use the water directly from the sinks for irrigation, or do we have to filter it first. I have seen grease traps and sand filtration techniques used for other gray water treatment, but because our water is only from hand washing, I am under the impression that I do not need a filtering system. The irrigation would be for trees and bushes in the front of the building, and creeper vines that will grow along the walls of the building.

We want to build economical and environmentally friendly water conservation/recycling systems. We basically wanted to know what we could do, and what the general costs would be for installing a Grey Water system.

Solon Stewart




Dear Solon Stewart,

Our Ngo has been implementing wwt systems employing natural methods on black & grey, part black and grey, and only grey types of waste-water.

We have observed that the waste-water requires to have some minimal amount of black element i.e bio-remains.

If only grey-water is to be processed, some bio-slurry is to be added with the periodically for the process to be effective.

We employ a plantation-bed and these plants take care of cleaning up the water.

Thus fairly clean and clear re-use water is achieved which can be used for toilet flushing, irrigating horti-culture and other lower-end uses Etc.

In our earlier responses, we have given more information on the wwt-process and other details.

This website may be referred for the same.

For more specific details you can be in touch with us.

with wellwishes from VigyanVijay,
Ajit Seshadri

Er. Ajit Seshadri,Head- Environment, The Vigyan Vijay Foundation


Dear Solon Stewart,

You are right that you do not require any grease trap/sand filter etc, but what you forget that in your rest room in the wash basin you do use soap for handwashing.

Instead of using this water directly for gardening, you could collect it in a buffer tank, and then allow it to gradually pass is through a gravel bed which you could use also as a flower bed, with Canna's planted . Cannas are used to extract many undesirable pollutants in a wetland environment as they have a high tolerance to contaminants.

This kind of treatment is not really something which is very costly or difficult to execute., the cost would be the cost of the buffer tank on one side and on the other side the main tank where you could have the water collected ( size of this depends on the maximum daily water consumption- and daily water use for irrigation).

Naturally there will be a time delay from the time you put water in to the buffer tank till the time a substantial amount is collected in the collection tank . This depend upon the length of the gravel filter bed that you have in between and the gradient.

As you have not given any figures as regards the daily water use and irrigation water requirements I am not in a position to make any suggestions regarding it.

Dr. Anil Lalwani


Dear Solon Stewart,

The quantity of gray water generated is not mentioned and the area of irrigation. Assuming wastewater generation not exceeding 5000 litres your gray water can be used for irrigation in your case after simple filtration mechanism.

The raw effluent may contains soap and detergent matter which contributes to increase in suspended particles and oil and grease which may lead to choking of the soil through continuous use. Intermittent use of fresh water will provide a breathing period for the soil to recover from the effects of continuous loading.

With regards,

M. Karthik
Scientist C
Waste Water Technology Division (WWT)
National Environmental Engineering Research Institute


Dear Solon,

Before taking a final decision, guaging the volume of water this can generate should be an important step.

In general if it is only hand-wash water (meaning the key contaminant is going to be soaps and detergents) and its volume is relatively low, redirecting it to the garden directly is possible. However also choosing the right plants such as banana or canna which thrive on the phosphates from soaps and detergents will be good.



Dear Sir,

If the Grey water is only from the wash basins in the restrooms, then it is fine that we can go ahead with the idea of using the same for irrigation purpose for the trees inside the campus. The only precaution needs to be taken in this respect is that there should be any localised ponding or splashing from such irrigated water. For this purpose, drip irrigation method in control manner may perhaps be helpful.

Such approach will be cost effective also, because this can be achieved by utilising PVC pipes also.

Thanking you for your Environment friendly approach for conservation of water.


Dear Solon Stewart

No problem you can use this water directly.

With regards

S. Vishwanath
Rainwater Club

7. Gray water purification

Hello All,
We have been facing water problems in our apartments very badly in the recent past though we have implemented rain water harvesting methods.
Now we are trying to explore if there is any way we can purify grey water, either natually (can we route the gray water pipes to a location in our apartment where they can get absorbed into the ground) or through any device. If we need to use any device, how much does it cost to implement the same.

8. Use soil space in the garden, sunlight and plants to recycle

Pl let me know how many are the apts and what is the normal total occupancy.

You can easily clean the water used for bathing and washing of clothes by a simple soil process which uses soil space in the garden, sunlight and water loving plants. The soil space needed is 2.5 sq ft per individual. This will enable you to recover about 60% of the water used. It operates on gravity and is practically self-sustaining.

Give me details and I will give you more info.

Indukanth Ragade(

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