Grey water is the water used in households which isn’t part of the sewage system waste water. Think of the water you use when you take a shower, bath, wash your hands, do the dishes, wash the car, or do your laundry. Approximately two-thirds of a typical household’s indoor water usage is grey water. Think about how much of a saving this represents if you put your grey water to good use.
You can reuse grey water to flush the loo or irrigate your garden. This keeps the water onsite instead of funnelling it into the wastewater system, which means it doesn’t have to be sent through water treatment and purification plants which ease the burden on the plants and ensures clean water can be used more efficiently for human consumption and medical use.
In the UK grey water technology is still in its infancy, largely because it is still so expensive, for example, Cambridge Water Company estimates that a grey water recycling system would add £5000 to £6000 to the cost of a new property. Installing a system would cost upwards of £3000 and then you have to consider maintenance costs. Currently, the payback period on a grey water system is about 10 years, which, unfortunately, can be longer than most systems will last. If you have the cash to spare, however, using grey water can reduce your monthly water bill.
Another inhibiting factor has to do with health; there are concerns that using grey water around the house poses health risks to all those who live in it, especially children and pets. A potential danger of using grey water in your garden is the build-up of bacteria which could affect the health of pets and children who romp around the lawn.
There are benefits
Having said all that, there are still benefits to recycling your grey water. Cambridge Water is one of the leading voices in the field and actively encourages incorporation of grey water systems in new-builds and according to the company, the best way to eliminate risks and maximise cost-efficiency is to use water efficient appliances in combination with a simple grey water system that works on a basic filtration system. Systems collect wastewater from baths, showers and washbasins, after which it is treated and pumped into a storage tank which is connected to the toilet’s flushing system or garden irrigation system.
More sophisticated grey water recycling systems are required for bigger properties as more stringent biological methods are used to ensure the correct treatment of the nutrients in the wastewater to prevent bacterial build-up. These larger systems use a method comparable to the processes and methods used at sewage plants. Some systems combine the filtration system with the biological treatment and add bleaching agents to stop the growth of bacteria once the water is in storage.
iRain Water Harvesting provides some figures on residential water use that show exactly how much of your water is going to waste.
• Bath: 80 litres
• Shower: 30 – 35 litres
• Single toilet flush: 8 – 9 litres
• General water use: 25 – 30 litres
• Washing machine: 60 litres
• Dishwasher: 40 litres
• Watering the garden with a watering can: 7 – 9 litres per full can
• Washing the car with a bucket: 15 litres
Of those, bath water, shower water, general use, washing machine and dishwasher water can all be recycled as grey water. That’s 250 litres of water that can be reused! Before you install a grey water system do your homework and make sure you have an accurate assessment of just how much water you’ll be able to save, and how much this will translate into cash in your pocket from the savings on your water bills. But remember, it’s not always about saving you money; sometimes it’s about saving the planet.