Gray water: how to use reuse water
Learn how to reuse gray water from the shower and washing machine
Cistern used for the storage of reuse water in Brasília. Image: Pedro Ventura/Agenzia Brasília
Using reused water, or gray water, is synonymous with saving against waste and, together with other practices such as reducing the consumption of meat and animal derivatives, is a form of environmental preservation.
Saving water is an important measure for environmental preservation. Paying attention to the resources that come out of your drains is the first step to reduce your water footprint (which also involves the water consumed indirectly, that necessary for the existence of the products and services you use).
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Much of the water used in a house is thrown away with very little waste and could serve as reuse water for flushing, washing floors, watering plants or washing the yard. To wash 8 kilos of clothes, for example, about 100 liters of water are used, a volume sufficient to give 16 flushes. (See some tips on how to reuse gray water in condominiums.)
This is what is called gray water, a type of reuse water from baths, washing machines and bathroom sinks. They are those waters that have not come into contact with black water (those mixed with feces and urine). These reuse waters look and smell different depending on where they come from and what chemicals are mixed with them. (Understand the differences between gray water and black water).
We have prepared a manual to help you deal more consciously with water waste from your home, learn how to store and treat this reuse water and know where it may or may not have a new use.
Types of gray water
Reuse water (grey water) from the bath usually has a light gray appearance. It may contain soap, shampoo, and body secretions such as sweat and skin oils. Like other gray waters, they can also contain microorganisms such as bacteria, fungi and viruses. In the case of washing machines, each operating step (washing, rinsing and centrifugation) produces water of different qualities and appearance, with different reuse possibilities.
Main reuse options
Some of the main options for the reuse of greywater are the use in sanitary discharges, cleaning floors, walls, yards and vehicles. It is necessary to be aware of the types of chemical products present in each of the reuse waters, to avoid the risk of stains on the floors, wear on the car's paintwork or contamination.
How to collect reuse water
The water from washing clothes in the machine can be collected through specific cisterns for this reuse or even with homemade buckets, varying the sizes according to the amount of clothes in each cycle and the size of the machine. Any of the options must be linked to the machine's water outlet, and the water can be separated by cycle or not.
The residual water from the shower can also be collected with buckets and basins, positioned in places with a greater volume of runoff. If you have a bathtub, just collect the water that was left inside after the bath to reuse it.
Once collected, these reuse waters can be stored in cisterns or collection gallons. The important thing is that the reservoirs are closed to keep the mosquito Aedes aegypti away, rest on a flat surface and out of contact with children. If the container has a tap at the bottom it is better - both for water reuse and cleaning.
One option for quickly treating gray water, tested by the Technological Research Institute (IPT) at USP, is to mix 5 mL of bleach for each liter of reuse water stored. This will prevent or lessen the emission of unpleasant odors when dark gray waters (those with a greater amount of waste) are stored for later use. But this is not a completely safe formula, as it would be necessary to know in detail the composition of each gray water. Download here your complete Manual for the reuse of gray water.Watch a video (in English) about reusing gray water in the bathroom.
