Greywater is the waste water generated from dish washing, laundry, baths and showers. It accounts for about 50-80% of residential waste water. Greywater gets its name from its cloudy appearance and it is neither fresh (drinkable tap water), nor heavily polluted.
Around the world, the majority of greywater ends up as effluent in rivers and oceans. In the UK this waste water generally enters the mains sewerage system. In recent years, the cost of domestic mains water has resulted in many people using it for irrigation, especially when areas are hit by hose pipe bans. Typically it is siphoned out of baths or transferred using buckets.
From an environmental perspective, dumping greywater onto the soil is less damaging than sending highly treated greywater directly into natural waters. This is because because the soil acts as a natural filtration system. Using it to irrigate plants is another way to use it as the plants use the alleged contaminants of greywater, such as food particles, as nutrients. Treating greywater before using it to irrigate plants is like treating water then pouring it into the drain. It's a waste of time and resources. There are limits as to how much greywater can be deposited onto the soil though.
Using greywater is a lot simpler if you can syphon it into a holding tank, from where you can then use a bucket or watering can to distribute it around the garden. It also saves you having to wait whilst water syphons out of the bath, a process that can take a while if you are using a narrow bore hose pipe.
In the real world, capturing greywater on a daily basis can be the difference between keeping your garden alive during the dry summer months and not. We currently live in Suffolk, which is one of the drier parts of the UK and using greywater on the plants in our garden has kept them alive each summer. The other advantage is that you can legitimately use this water when a hose pipe ban is in place. Any excess can also be drained on to a lawn.
You can collect greywater from the following sources:
To put some of the volumes into context, we have a standard bath and a corner bath in our current home. Each is used at least once a day and the shower is used once or twice as well. A typical bath uses about 60 to 90 litres of water and a shower around 30 to 40 litres. This means that the water used each day for baths and showers is over 200 litres. This means that you need a reasonably large tank to collect it all over the course of a day, for temporary storage and subsequent distribution. A watering can holds about 10 litres, a standard dustbin will hold 80 litres and a standard water butt is typically 210 litres. The normal recycling 'wheely' bins used in the UK are 240 litres.
Adding the pipework into a new build to reuse grey water is a relatively simple and cheap thing to do, as most of the pipework would already be required to take the water to the sewerage system (black water).
Most domestic greywater is easy to treat and recycle, due to their lower levels of contamination. However, entirely untreated greywater is still considered to be a potential health and pollution hazard, because studies have established the presence of the same micro-organisms within greywater as found in sewage (albeit in much lower concentrations).
If collected using a separate plumbing system from blackwater, domestic greywater can be recycled directly within the home, garden or agricultural company and used either immediately or processed and stored. Recycled greywater of this kind is never clean enough to drink, but a number of stages of filtration and microbial digestion can be used to provide water for washing or flushing toilets; relatively clean greywater may be applied directly from the sink to the garden or container field, as it receives high level treatment from soil and plant roots. Given that greywater may contain nutrients (e.g., from food, fertiliser, etc.), pathogens (e.g., from your skin), and is often discharged warm, it is very important not to store it before using it for irrigation purposes, unless it is treated first.
Most UK houses would benefit from grey water capture and reuse. In our current home it enables us to keep our garden alive during the driest months of summer, even in the relatively arid conditions often encountered in Suffolk (East Anglia). It really is quite amazing how much water gets poured down the drain an average sized family (four in our case).
