Hesperian Health Guides
Wastewater: A Problem or a Resource?
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Because the amount of water in the world stays the same, all water is used over and over again. But runoff water and water that has been used for washing, farming, sanitation, or industry often contains germs and chemicals that make it unsafe for drinking, bathing, or washing.
Water that is not contaminated with toxic chemicals or human waste can be reused after simple treatment. The method best suited for your household or community depends on the amount of wastewater to treat, what it is contaminated with, what it is to be used for, and how much time, space, and labor you have to treat the water.
Greywater is wastewater that has been used for washing and other household chores, but does not contain human wastes. As long as you do not use toxic soaps or cleaners (see “How to make safer cleaning products”), greywater needs only simple treatment before being reused in the garden, or no treatment at all before being disposed of into the ground.
There are many different types of greywater systems (see Other Water and Sanitation Resources). Any greywater system works best when:
- it is easy to build and maintain.
- grease, concentrated bleach, solvents, and other chemicals are kept out of the water.
Constructed wetlands (reed beds) filter greywater
One way to treat greywater is to copy nature's way of cleaning water by making a wetland. Constructed wetlands (also called reed beds) treat greywater by filtering water through layers of plants, soil, and rocks. Nutrients in the wastewater feed the plants, and the plants add oxygen to the water, which helps clean it. Reed beds also:
- provide irrigation water for food crops.
- grow plants you can harvest for other uses, such as bamboo or reeds.
- replace stagnant water with beautiful gardens.
To make a constructed wetland
In planning a constructed wetland, consider these issues:
- How much area do you need and how deep does it need to be? The more water that flows through the system, the bigger and deeper it needs to be to safely filter greywater. If water flows too quickly, the reed bed cannot clean it well.
- Is the water source higher than the wetland? Water must flow through the wetland, so it needs to come from a source above, or be pumped.
- Where will cleaned water flow to? Can it be collected in a storage tank or directed to a garden?
Wetlands can be built anywhere there is enough space. If there is little space, they can be built above ground in basins, such as a 200 liter drum. In areas with well-drained soil or high groundwater, dig a pit and line it with thick plastic or cement. In areas with clay soil, no lining is needed.
To maintain a constructed wetland
A constructed wetland dug into the ground can treat large amounts of greywater.
Every constructed wetland has different needs depending on the amount of water, the type of soil and plants, and other conditions. Experiment to find the best way to make your constructed wetland work.
- If plants dry out or die, not enough water is running through. More water sources can be added to the system, the pit can be made smaller or less deep, or new plants can be added.
- If water does not flow through, try bigger stones and less sand, or lower the outlet pipe.