Using Greywater in the Garden

Greywater is domestic waste water from activities such as laundry, dishwashing, and bathing. Unlike sewage water (which is referred to as blackwater), greywater can be safely recycled for use in the landscape without the use of any special treatment systems. Because we use large amounts of this type of water for daily household activities the average bathtub uses 26 gallons, in extreme drought conditions greywater can be a great way to conserve water.

Greywater to Use and Greywater to Avoid:

The organic contaminants in some greywater, such as food particles, can supply plants with valuable nutrients for growth. However, greywater that is heavily contaminated with salt, soap residues, fats, or grease can be toxic (to both microbial and plant life) and should be avoided. Some types of domestic greywater are better than others for use in the garden. In order of preference they are: shower, bathtub, bathroom sink, and utility sink, provided bleaches or strong detergents have not been used. Water from dishwashers and washing machines is not safe to use as it contains too much detergent.Depending on your home's air quality, the water you collect from your dehumidifier may also be used. In fact, water from this source can actually be better for your plants than the water from your tap. Unlike tap water, a dehumidifier condenses water vapor out of the air so it contains none of the dissolved minerals that are sometimes present in tap water. It's unsafe for human consumption as there may be bacteria growing in it, but it should be fine to use on your plants.

Do NOT use greywater on the following:

• Edible fruit, vegetables, or herbs.
• Acidic soil-loving plants (detergents are alkaline).
• Newly propagated or container-grown plants or plants grown in a greenhouse.
• Grass.
• Areas where it might form puddles that attract playing children or thirsty animals.

Tips for Using Greywater:

• Greywater can be transported directly to the garden from a bathtub (or sink) in a bucket, or the water can be diverted from your plumbing to the garden using a hose. Pipe diverters, available at hardware stores, are used in the same way as rainwater diverters from a downspout. They can be fitted to the waste-water drain from the bathroom and fed into an outdoor barrel or container dedicated for greywater.
• Always store greywater in a dedicated container fitted with a lid, and use it as soon as possible after it has cooled. Because greywater contains organic solids, it can become smelly and unpleasant (and provide a breeding ground for disease pathogens) in only a few short hours.
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• Apply greywater to the soil near the plant, never directly on its foliage.
• Do not use greywater containing bleaches, bath salts, artificial dyes, cleansers, and products containing boron. Avoid sodium-based detergents. Instead, use all-natural, biodegradable soaps with ingredients that are labeled safe for the environment.
• Avoid using greywater with dripper or fine nozzle irrigation systems, which can become clogged by suspended particles in the water.
• To prevent harmful salts from building up in the soil, alternate applications of greywater with other irrigation methods.