Determine the Effect of Gray Water on Plant Growth

What You Need to Know

Gray water is used household water that does not include sewage (toilet water), otherwise known as black water. Gray water is nonpotable, meaning that it is not fit for drinking.

How Does Gray Water Work?

Gray water is used household water, such as from sinks, bathtubs, showers, and washing machines. In some dry climates, houses have plumbing that allows the gray water to be reused as shown in the figure on below. Pipes carrying gray water are labeled so it is clear that the water is nonpotable.

What Does This Have to Do with Plant Growth?

Water is necessary for plant growth. Some people use gray water to water plants. Gray water often has different kinds of soap (washing soap, hand soap, bath soap, shampoo, etc.) in it. Do these solutes affect plant growth?

Fun Fact

It is estimated that 42 to 79 percent of household gray water comes from the bathtub and the shower. Taking a "navy shower," which allows the water to run no more than 2 minutes, can save on water use. For this type of shower you turn the water on only to get wet and rinse off. The water does not run while you soap up and scrub your body.

Real-Life Science Challenge

Is it safe to use gray water on plants? Kitchen gray water should not be reused because the food particles in the water decay. The bacteria causing the decay could affect the plants' growth. Gray water from the washing machine should not be reused if it is contaminated by soiled diapers or clothes, materials used by people with infectious diseases, or materials used in poultry or wild game preparation. The health risks from gray water are considered minimal if you handle and apply it properly. Six basic precautions when using gray water are:

1. Use it the same day it's collected.
2. Don't apply it where people will come in contact with it, such as on a lawn.
3. Don't use it to water food crops.
4. Don't let it puddle or stand. (Make sure it is absorbed quickly.)
5. Don't spray it or sprinkle it in any way. Instead, pour it.
6. Whenever you handle gray water or equipment that's in contact with it, wear rubber gloves.

Experiment

Now, start experimenting with how gray water affects plant growth.

Hints

• Determine the best way to collect gray water.
• Use different sources of gray water to determine its different effects.
• Use the same type of plant.
• Control variables like the amount of water, the method of watering, and so on.

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