Menu Close

Why use greywater?

    • Greywater systems are one of those things that many plumbers try avoid, because of several issues associated with it
    • Greywater can be used water from a bath, shower, washing machine or similar sources – and is sometimes confused with toilet water which is black water
    • Greywater is a cheaper form of alternative water – by using greywater consumers can reduce their potable water demand, and their bill

Greywater systems are one of those things that many plumbers try avoid, because of several issues associated with it.

Greywater can be used water from a bath, shower, washing machine or similar sources – and is sometimes confused with toilet water which is black water. Kitchen wastewater is also regarded in that category because of the amount of fat and food residue in the water. There are instances where kitchen water goes into a greywater system – but in that instance the user needs to ensure that whole fats and raw food do not go down the drain. That needs to be managed on site.

Greywater is a cheaper form of alternative water – by using greywater consumers can reduce their potable water demand, and their bill. If one recalls, for instance, the recent water restrictions in Gauteng where areas were without water for some time, greywater systems could keep a household going a day or two without water. It can be used at least for toilet flushing so at least you can have sanitation, and other non-potable uses such as garden irrigation – anything where there is no direct human contact. However, it is not drinkable and I would not recommend using it for showers.

It can reduce water consumption in commercial and domestic buildings by reusing greywater and rainwater on site, thereby giving the municipal system a chance to recharge. That means one can reduce or even avoid cuts from the municipal supply by using it as an option to reduce intake of water from the municipality.

For toilet flushing, obviously there needs to be a pipe system to give the toilets a separate supply to the rest of the house. Even for garden irrigation, untreated greywater can be a problem – as the home residents have to keep clear from it when starting up the irrigation system.

While it is possible to treat greywater to drinking water standards, it comes at a cost. The low-hanging fruit is to use greywater for non-potable purposes and continue using municipal water for portable purposes. The use of untreated greywater is problematic – and when talking of greywater most people think of untreated greywater. It cannot be stored because of the bad odour after two or three days and it can also block up irrigation systems. In contrast, treated greywater does not have a bad odour and can be stored for extended period of months at a time, and can be used for an array of non-potable uses. It will not clog up the irrigation system or a toilet.

When looking at the cost and payback period for a greywater system, it obviously saves on water bills. In addition, many municipalities – including Johannesburg and Cape Town for instance – charge sewerage as a percentage of your water usage. This means residents can enjoy a double saving not just on purchasing water, but on the sewerage charge.

Greywater might contain harmful bacteria, so if you use it for floor washing, I would recommend disinfecting it with UV. For normal irrigation purposes, normally disinfection is not needed. For toilet flushing, I would recommend adding a bit of chorine to keep everyone safe.

We built our first greywater system back in 2003, a typical anaerobic system whereby you couldn’t store the water for long and it potentially blocked irrigation systems. We started improving on that over a period of 12 years. The current domestic model was built in 2015 with the first version installed in January of 2016 for the first time and has been running now for almost seven years without a glitch. This model has set a new standard in greywater.

Greywater systems need to be relatively cheap to treat water, achieving the ‘sweet spot’ wherein the maintenance is low, the operating cost is low, and you get a good usable water quality on the other end.

There are three types of greywater systems that we build:

    • Anything from 1 500 up to 7 000 litres per day. If you have an irrigation system that is not irrigating every day but the system discharges 400 or 500 litres a day to the greywater system, then you can accumulate it for three days in order to do a proper irrigation. Without a storage capacity you would need to irrigate every day or a couple of times per day and then not get proper saturation of the soil. It is better to store the water for a number of days and then irrigate for proper saturation.
    • Commercial and industrial – this we design to customer requirements on a case by case basis.
    • The domestic system: the sub-surface model (we also do above ground if needed) comes as a pre-manufactured unit. The installer digs a hole, drops it in with an inlet pipe, a vent pipe overflow to the municipal sewer, an airline connection and the suction pipe for the pump. There are five connections to make and the entire system is up and running.

First there is a baffle that separates the incoming water from the irrigation water. They also have a lint filter that ensures the lint from your washing machine stays behind in the chamber and the overflow will run to the sewer. Any body lotions and body fat in the water will float to the top and overflow to the municipal sewer system.

Sand and grit will settle at the bottom – so in a non-domestic setup you would have to pump that out after about three years, though to play it safe I would recommend once a year.

We have an option whereby a rainwater system can be added. It is designed so that once the chamber fills up, the rainwater will overflow to the storm water and incoming greywater will overflow to the municipal sewer. There will never be a risk of greywater ending up in the storm water system or stormwater ending up in the municipal sewer, which is prohibited in many municipal bylaws.

This system can be connected to the automatic irrigation system. For normal greywater systems that cannot store water there is no point in connecting it to the automatic irrigation system because the minute you start it up there is not enough water. The entire system runs itself without any no human intervention, except maintenance.

What solution a plumber can typically offer customers in water scarce areas – is a rainwater harvesting system that goes into the house and a greywater system for the garden. Such a system needs minimal water from the municipality. Optional to the greywater system – which is not standard because of the price – is a panel designed for everything to be connected to run the entire greywater system.

There are ways to cater for it where the greywater tank needs to be in a driveway. The tanks are made of plastic, so you can walk over it and kids could play over it, but you cannot drive over. If you want to drive over it there are two ways to do that: the one is to cast the white bearing slab over the plastic tank: the second would be to construct a concrete tank and build the greywater system into that.

Benefits of using greywater systems:

    • Reduce municipal water demand
    • Conservation of freshwater
    • Greywater can be re-used for toilet flushing
    • Use for garden irrigation.
    • Groundwater recharge
    • Reduce strain on sewage systems and septic tanks

Features and Specifications

    • Fully assembled, ready for drop-in on site
    • Good quality underground tank ensures durability
    • Only the green lid will be visible
    • Risers can be used to raise lid to ground level if tank is installed deeper than chimney height
    • Air pump uses only 40 watts of power
    • No bad odours
    • WW1 Filter is easy to clean.
    • Up flow through WW1 filter ensures minimum cleaning intervals.
    • WW1 filter turns first chamber into a grease trap, thus separating fats from your irrigation water – domestic use only
    • Both Grey Water and swimming pool backwash water can enter the tank.
    • Overflow goes to municipal sewer
    • Surface (JET) or Submersible (Citypump) can be used
    • For irrigation, add a good irrigation filter after the pump
    • UV is optional
    • Very low maintenance
    • Rain water harvesting can be incorporated. When full the inflows are split through internal valves and grey water overflows to the municipal sewer line while rain water overflows to storm water.

By Eamonn Ryan, based on a Tech Talk presentation by Gerhard Cronje of Maskam Water on greywater systems and their offerings

Leave a Reply

Your email address will not be published. Required fields are marked *