When looking to reduce your municipal water footprint, you are generally presented with two excellent options: harvesting rainwater from your roof, or recycling graywater from inside your home. Both are incredibly eco-friendly, but they have distinctly different rules, uses, and limitations in the garden. Let's explore the differences.
What is Graywater?
Graywater is gently used water from your bathroom sinks, showers, tubs, and washing machines. It is not water from toilets (which is called "blackwater" and contains feces) and it usually excludes water from kitchen sinks or dishwashers (due to high organic load and fats).
The Case for Rainwater
Harvested rainwater is essentially distilled water provided by nature. Aside from whatever it picks up on your roof (which is easily handled by a first flush diverter and debris screen), it is exceptionally pure.
- Pros: Plants love it. Rainwater is slightly acidic and free of chlorine, making it the highest quality water you can provide your garden. It can be sprayed through sprinklers, stored in tanks for months without degrading, and used on any edible crop.
- Cons: It is entirely reliant on the weather. In a severe drought, your rain tanks will eventually run dry right when your garden needs water the most.
The Case for Graywater
Graywater is a constant, guaranteed supply. Even if it hasn't rained in six months, every time you take a shower or do a load of laundry, you generate water.
- Pros: It is drought-proof. A family of four can easily produce 100 gallons of graywater a day. It is an incredible resource for keeping fruit trees, bushes, and lawns alive during harsh summers.
- Cons: Graywater contains soaps, dead skin cells, and trace bacteria. Because of this, the rules for using it are strict:
- You cannot store graywater. It must be sent directly into the yard immediately. If left in a tank for more than 24 hours, the bacteria rapidly multiply, smell awful, and essentially turn it into dangerous blackwater.
- You cannot use overhead sprinklers with graywater, as it could spray bacteria onto people, pets, or into the air. It must be delivered sub-surface or via drip lines covered by heavy mulch.
- You cannot use it on root vegetables (like carrots or potatoes) or on the edible parts of leafy greens. It is best reserved for ornamental plants, fruit trees, and lawns.
The Ultimate System: Combining Both
The most resilient sustainable gardens utilize both forms of water in a dual-source strategy.
Use your Rainwater on your vegetable beds, your delicate seedlings, and in your greenhouse. It is clean, safe for food crops, and easily pressurized.
Use your Graywater to heavily irrigate your thirsty fruit trees, perimeter hedges, and ornamental lawns. By redirecting the washing machine discharge pipe out the window into a mulch basin surrounding an apple tree, you ensure the tree thrives all summer while saving your precious rain tank reserves for the tomatoes.