To say rainwater harvesting is a hot topic is an understatement…

harvest rainwaterSouth Africa is an arid country and our water resources are not well managed. Capetonians have recently had to make do with 55 litres per person per day. Think about this, how would your household cope?

Let’s look at going to the loo…

A standard toilet requires 13.6 litres per flush a low flow toilet uses 6 litres per flush. If the average person flushes the toilet 5 times per day that is 36 litres already if you have a low flow toilet.

Coping on 55 litres a day is a real struggle. Have a look at this graphic, 1 machine load of washing a week… eek!


The value of becoming self-sufficient is very evident!  In the long run it’s also a more sustainable approach. Consider a rainwater harvesting system if you are planning to build a new home, a renovation or want to be self-sufficient.

Now, you might be thinking, but how complex can this be you stick rainwater tanks everywhere, right? This is one approach but as I learnt there is a better approach! When researching rainwater harvesting I found it difficult to get useful information. This is because the principles are simple and specialists don’t want to share them for fear of losing work.

While the principles are simple the implementation, fittings and systems require knowledge. When investing in a rainwater harvesting system, I’d recommend appointing a specialist.


As much as we South Africa’s hate to admit it Australia is way ahead of us, especially in sustainability. Due to Australia’s dry climate they have rain water harvesting regulations. South Africa should follow suite. Most of my research is from Australian systems because they are so simple yet so effective! At the time of writing, SA does not have domestic rainwater harvesting regulations. Draft regulations are being promulgated.


Explained simply, a wet system has one water storage location with all

water fed to it via a system of pipes.

The advantages of this are:

  1. One pump and filtration system can service the entire system.
  2. Easy monitoring and maintenance.
  3. Ugly tanks need not be all over the place.
  4. No gutters and rainwater pipes at odd angles.
  5. Tanks can be where there is adequate space
  6. Design of the building is not compromised.

How it works.

  1. All roofs feed water into a pipe system that runs below ground to the tanks
  2. Tanks are in one location and are all connected to each other.
  3. The pipe system feeds water into one or two tanks.
  4. The pump and filters connect to the tanks and this feeds the house.

First let’s start with the feeder system of pipes. The idea is that you have an underground pipe system that connects to the tanks. It’s important that the pipes are adequately sized to take the amount of water that will be coming off your roofs. Your Rainwater harvesting specialist will calculate this.


The pipe system works on a gravity feed and needs no pump! The system will only work if your outlet point (into the tanks) is lower than your inlet point (where water enters). This is critical to the systems success and blew my mind when I first discovered it!


Very important to the water quality and longevity of the system is to keep debris out of the system. This starts with the pipe system.

Mesh filters at the top of the downpipe keep leaves and other debris from the roof and gutters out of the system. A rainwater head installed at the top of the PVC downpipe does this.

In Australia gutter have mesh over the top to prevent debris. I am yet to see this in South Africa.

The Australians also make use of a first flush system. A first flush system diverts the first water containing dust from roofs out of the pipe network.  The remaining water goes to the tanks.

Besides mesh filters at the head of the pipe system a second in tank filter is recommended. The filter sits in the top of the tank that water feeds into. It dispels debris out of tank and drops the water into the tank. There are many systems and your specialist can advise you. These are all classified as sediment filters.


When it comes to your tanks you have a many options.

  • Plastic tanks
  • Steel tanks
  • Plastic underground tanks
  • Underground reservoirs

I favour plastic rainwater tanks in a tank yard. Seeing as you are piping the water to your tanks you can place them anywhere and can hide them. In the image below the tanks are behind a screen that forms part of the entrance.


Some people favour an underground reservoir, as tanks tend to take up valuable space. I have reservations about this. First it’s very expensive.  Second, when it leaks the entire reservoir will be drained to find the leak. This is arduous and expensive.  If underground storage is the only solution I would place my tanks inside the reservoir.  This eliminates a lot of future issues.

Bear in mind that an underground reservoir also still needs an overflow. Compact, slim-line tank options can fit in a skinny side space. Your specialist or architect can advise on tank placement.


To use your water in the house you’ll need to filter it. What you intend to use it or will determine how well you need to filter it.

You can use your rainwater for:

  • Irrigation
  • Flushing toilets and laundry only (the biggest consumers of domestic water)
  • To top up your pool
  • Throughout the house

If ou plan to irrigate with the water your rainwater heads will be enough.

If you plan to use the water for laundry and flushing you’d need rainwater heads and in-tank filtration. This will ensure no debris gets into your appliances.

If you want to use the water in the house you would need: rainwater heads, in tank filtration and a triple carbon and UV filter. That is what I have shown in the image, a system for full ‘in- house’ use.

Your rainwater specialist will be able to advise you on the best solution to meet your needs and budget.



Depending on your location and your rainfall season you may need a municipal backup. This will be for when there are lengthy dry periods, or for when service delivery fails.

Municipal backups can be configured in a variety of different ways. This will depend on your requirements.

  1. You could have a manual or automatic switch over switch, for when your tanks are empty.
  2. If you’d like a backup for when there is a disruption in supply, you can have a small tank that only holds municipal water. This gets used when there is a disruption in supply. Or you can opt for a percentage of your tank system to be municipal water.

Once again your specialist can tell you what is best suited to your requirements.


As with all things your rainwater harvesting system will require some maintenance. For better water quality and tank longevity aim to keep debris out of the tanks.   It forms a layer of organic material at the bottom of the tank that affects water quality. Tanks need to be monitored and will eventually need to be cleaned out.

Your filtration system will require maintenance every 6 months, to ensure that your water is filtered properly. The pump will also require maintenance at intervals.

Maintenance periods can be prolonged by reducing debris through mesh and filtration.


Many people use rainwater as a means to irrigate the garden. This will reduce filtration cost.  Irrigation uses a higher volume of water than the household. My personal view: I’d rather be able to shower, do my laundry and flush the toilet than water the lawn when there is an interruption in service or water restrictions. Think 50 litres a day per person…

My personal view is that if you are going to invest in a rain water harvesting system rather use it in house.


At the time of writing this article, a complete system excluding tanks costs about R100k. This would also exclude your gutters. This cost will vary depending on the size of the system and what the water is being used for.


If you are planning a new home, consider including rainwater harvesting. Even if you only install the system at a later stage. Or if you are considering rainwater harvesting to avoid inconvenience.

From a practical point of view I’d recommend the wet system explained in the blog. A wet system is also much easier to retrofit as placing the tanks becomes much easier. If you do not want to rely on municipal services, be affected by water restrictions and reduce your water bill rainwater harvesting is a definite consideration.


We have worked with and can recommend these two specialists:

GraTech: Etienne van der Merwe – etienne@gratech.co.za

Peaceful Landscapes: Kristen Kallesen – kristen@peacefulscpes.co.za