Purification Of Recycled Greywater

Posted on: 18 February 2015

In today's energy-conscious environment, it's important to recycle as much as possible. This isn't limited to scrap metal and plastics; even water can be recycled. Greywater sources such as laundry and bath water can be easily recycled and used in a number of ways. However, the majority of greywater applications will require treatment prior to use. 

Greywater Disinfection

Although there are a number of water-treatment options becoming more readily available -- such as UV, Ionic and O-zone treatment -- the two most widespread approaches involve either chlorine or iodine. 


Chlorine is by far the most common approach and the is the method used to disinfect swimming pools for public use. Additionally, chlorine is readily available and is found in household bleach. It has numerous properties that make it a great option for disinfecting water - it's cheap, can be stored for great lengths of time, and most of it will turn to vapor after treating the water. 

Greywater is full of organic material, which will combine with the chlorine after it has been added to the water. This can significantly reduce the amount of chlorine that is readily available for disinfection, so steps must be taken to improve the chlorine's efficiency. The most effective way of doing this is by introducing a water filter into the system that blocks organic matter from entering the treatment vessel. Of course, this filter can quickly become clogged up from particles suspended in the water, so it's important to clean the filter ever few weeks. 


Iodine is the alternative approach taken to purify water. This chemical is a slightly better performer than chlorine as it doesn't combine nearly as much with organic material. Additionally, it is a much better for disinfecting alkaline greywater, getting to work much faster than chlorine. With that said,  iodine is traditionally much more expensive than chlorine and is notoriously difficult to obtain.

Attempts are being made to make iodine treatment more readily available; however, at present chlorine reigns supreme. For this reason, the remainder of this article will focus on this approach. 

Chlorine Disinfection of Greywater

As mentioned, chlorine is the go-to approach for disinfecting swimming pools. Careful measurement has to be made when using chlorine as high concentrations of the substance can easily irritate the eyes and skin. You may have experienced this yourself when swimming without goggles; this is because the chlorine mixture has been too high for use. 

Chlorine Disinfection at Home

Commercial processing systems used in swimming pools will use an extremely high amount of chlorine; typically around 20mg for each liter of water. These commercial systems aim to free around 10mg of chlorine in the system after disinfection. However, when you're treating greywater at home you won't need anywhere near this amount. A good starting point for home appliances is one or two heaped tablespoons of chlorinated bleach for every five liters of water. The concentration won't be as high as in commercial appliances, but the chlorine will have a similar effect on the water. 

Chlorine Disinfection in the Yard

High concentrations of chlorine isn't only bad for the skin - it can be extremely harmful to plants. If chlorine is allowed to infiltrate the soil, it can slow down the ground's metabolic processes as it acts as a substitute for nutrients. 

If  you plan to use greywater for irrigation, then make sure to use it responsibly. Responsible use of greywater will not require prior disinfection, so you shouldn't have to worry about chlorination. Human bacteria that may be suspended in the water is not harmful to most plants, so disinfection may actually have a negative effect. If you must use chlorine-treated water, you should click here and store it for a day or two to allow as much chlorine evaporation as possible prior to application.