Day Zero still casts a long shadow


By Eamonn Ryan

Like mobile telephony two decades ago, the ultimate market size for rainwater harvesting and filtrations systems is unknown.

 RainblockDay Zero in Cape Town proved to be the catalyst for sharply increased residential demand for rainwater harvesting (RWH) systems with local suppliers of tank and filtration systems reporting exponential growth over the past year.

Figures of water tank sales supplied by the industry body, the Association of Rotational Moulders of Southern Africa, shows that growth in 2018 was 28.7%. Demand has doubled in the past several years, from 16 401t in 2010 to 32 000t in 2018.

Build It, a network of 300 hardware stores, reported that its sales of JoJo Tanks increased by 500% over the five years to end-2016. It has not slowed since, and most suppliers say demand is accelerating and they can scarcely keep pace with demand. One in every ten South African homes has a JoJo tank, which is reputed to have a 50% market share.

Reduced water availability at source – in dams and reservoirs – owing to regular drought conditions in one or another region of Southern Africa has resulted in many households and companies having to deal with the reality of water insecurity. There is a nationwide drive to reduce domestic water consumption to below the current average of 150ℓ (Cape Town at the height of its drought achieved 55ℓ). Domestic RWH is one such source of alternative water supply, focused on harvesting rainwater from rooftops. Other harvesting involves in-field, pavements and roads in the urban, peri-urban and rural areas.

A new trend?

Collecting rainwater for use in the garden is no new trend; it’s been done for decades. Placed under a gutter downpipe, a basic tank arrangement can be used to water plants and wash the car. A step up from this primitive system are RWH systems. These collect water in a similar way, then pass it through a filter to collect any debris or leaves. The water is stored in a tank, then pumped to feed a toilet, washing machine or dishwasher. Put simply, rainwater harvesting is the collection and storage of rain for a variety of uses – but not for drinking. RWH is a catalyst to dramatically increase household water security, while reducing the strain on drinking-quality water in the urban environment.

Fuelling demand for RWH systems is sharply increasing water tariff hikes, as well as concerns about the reliability, quality and quantity of water. For every 1m2 projected roof surface that receives 1mm of rainfall, 1ℓ of water can potentially be collected. A city house with a 150m2 roof surface that receives 10mm of rain can collect 1 500ℓ of rainfall.

This means, during a decent shower, a company can easily harvest 100 000ℓ in an hour from an industrial or warehouse-sized roof, for example.

Payback period

Current constraints for RWH success include justifying the capital outlay to install a well-designed and fully functional RWH system. The return on investment period for most systems at current water tariffs ranges from four to five years.

Wits School of Governance visiting adjunct professor and former Department of Water Affairs director-general Mike Muller has previously warned that RWH will not make a significant contribution to South Africa’s water challenges. The most important rainwater harvesting we do is capturing river flows in our dams. In years of drought, household RWH has less potential, “as it doesn’t solve long-term drought or mitigate significant water interruptions,” and most domestic RWH systems store less than 10 000ℓ – usually not enough to supply a household for more than a few weeks.

Sandy Ballam, director at Ballam-Waterslot, says, “The extended drought in Southern Africa, along with ever more stringent water restrictions, makes it very difficult to protect one’s not insignificant investment in a garden.

The solution is to install infrastructure which will save rainwater from run-off into the stormwater system and preserve it for use in the dry periods between rainfalls. The future savings on the cost of municipal water is obvious. Add to this, a leaf catcher that will prevent leaves and seeds from entering and rotting in the tank, and the very clever dirty water flushing device, which greatly reduces the dust and sands settling at the bottom of the tank.

“With the addition of a small booster pump, this water can be utilised almost anywhere in the garden. The pressure is sufficient to run a hand-held nozzle or a sprinkler,” says Ballam.

4evr’s Thintank can be used as a privacy wall or even in place of a border wall. Credit: 4evr

Talking standards

Since the publication of the SANS 1731:2017 tank standard in September 2017, seven South African tank manufacturers have been successfully audited by the Association of Rotational Moulders of Southern Africa (ARMSA) appointed independent auditing company, PESC (Productivity Engineering Services and Consultants).

The companies which lived up to the strict requirements of the tank standard are:

“We congratulate those tank manufacturers who have taken the lead in this independent compliance process,” says Wayne Wiid, ARMSA chairperson. “They have set the bar high for the industry. We urge other manufacturers to do the same because consumers and industry professionals have come to realise that without formal certification there is no guarantee that tanks manufactured comply with the standard and in turn no guarantee that the tanks will last.”


To use water in the house one needs to filter it. What its end use is determines how well it needs to be filtered.

Rainwater can be used for:

If the objective is garden irrigation, then rainwater is suitable and can be filtered to assist in reducing contaminants. If the water is also planned for laundry and toilet flushing, then rainwater and external filtration will greatly assist in ensuring that no debris goes into appliances where you run the risk of damage to the same.

Collecting rainwater for use in the garden is no new trend, it’s been done for decades.Credit: Cape Water SolutionsIf it is drinking water that is required then the water needs to be additionally treated, with chlorination being the most effective and cost-effective way of killing bacteria.

Global Water Solutions’ domestic filter range consists of premium quality housings, melt blown polypropylene sediment filters, as well as activated carbon cartridges. On the smaller RO units, there are also inline filters included, along with an RO membrane.

For domestic use, GWS supplies what it calls a ‘triple JUMBO (big blue) kit’, which filters water supplied to a house, depending on its requirements. For drinking purposes, a chlorine HTH (Scientific – specially designed by HTH for use in water storage tanks) floater would be put in the water storage tank to kill the bacteria. You would then filter the water through the ‘triple JUMBO (big blue) kit’ for filtering for all purposes in the house, including drinking.

In addition, GWS also offers a five-stage RO kit for inside, which is installed beneath the kitchen sink. This purifies the water to the purest and cleanest possible state that can ever be achieved, says GWS Regional Manager for Southern Africa Stuart Cooper. He adds that many people use this system on their municipal water supply without having the rainwater harvest component as they are not entirely comfortable with their municipal supply and the South African public is becoming increasingly health-conscious about the quality of their drinking water.

The three-stage filtration system consists of a 20 micron polypropylene filter for removing debris from the water, a carbon block and then a 5 micron filter. The system can handle a substantial flow of 20 to 280ℓ/minute, depending on the supply pressure.

In conclusion

Mike Muller says, “As a big picture person (more concerned about cities, rather than individual households) I am always keen to remind people that big dams are also a form of rainwater harvesting. So, I sometimes question the people who say that we must slow down stormwater runoff and let it sink into the ground (most of the time, it then evaporates (on the highveld at least), when we want to see it flowing into the rivers and dams!

“At a household level, it’s a bit like trying to go off-grid on electricity. It costs a lot and, very often, you still need to be connected to the grid during the long dry season. What happens then is that municipalities start charging a 'capacity charge' so you pay even if you don't use, just for the privilege of being able to connect to the grid when you need it.

“And when people have tried to work out whether there is really a monetary saving, the conclusion is often that it has not been worth it,” says Muller.