Rainwater Harvesting Systems – You may have by now heard the term “rainwater harvesting systems”, but you don’t 100% understand the term. Or you have heard the term and want to invest in such a system at your home? Well, in this article we will explain the full definition of rainwater harvesting systems, as well as the different types of systems you get in South Africa. This article will help you to make the decision on whether it is the right choice to invest so much easier.

What does the term “Rainwater Harvesting Systems” mean?

The term rainwater harvesting system, also known as rainwater collection systems or rainwater catchment systems, is technology that aids in the collection and storing of rainwater for human use. The rainwater harvesting systems range from the simplest form like barrels to more elaborate structures with pumps, tanks, and purification systems. Non-potable water is used to irrigate landscaping, flush toilets, wash dishes and washing the laundry. The non-potable water can even be purified for human consumption.

With the water scarcity that has become a problem for many populated regions, rainwater harvesting systems that are installed are able to supply households and businesses with water to use in the dry seasons. This lessens the demand for water on the municipal systems.

rainwater harvesting systems

What is the quality of the rainwater that is harvested?

Rainwater mixes with both soluble and insoluble materials from the surfaces. This means the water collects dust and pollutants as it flows down through the atmosphere. Contaminants may include plants, fungi, and other organic materials, as well as inorganic substances like dissolved minerals, metals, chemicals or water-soluble paints.

Rainwater that is collected for garden and agricultural uses does not need a high degree of purity. Although, rainwater that is collected from unclean surface runoffs, are not suitable for drinking or cooking with. You can improve the quality of rainwater that is harvested by separating the first flush of water from the roof, gutters and other collection surfaces from the rest of the water that goes into the water storage tanks.

And if I want to use the rainwater that is harvested?

If the rainwater that you have harvested is intended to be used for household applications, please note that it should then first be purified. Flocculation, settlement, and biofilm skimming are options you can use to remove bacteria, organic materials and chemicals that form films on the surfaces of the tanks or settle to the bottom, creating a sludge-like material.

Are chemicals needed to purify the rainwater?

A liquid alum solution can be added to the raw water. The purpose of this function is to bind fine suspended particles so that it forms a larger particle that can be removed by settling and filtration. This also removes the color, cloudiness, and aluminum from the drinking water you intend to use.

Pre-filtered water may then undergo solar water disinfection, or it will be treated with chlorine and other chemicals to kill infectious agents if the water harvested is intended for potable uses. There are a few other chemicals used to purify the water, like:

  • Potassium Permanganate
  • Calcium Hydroxide
  • Fluoride
rainwater harvesting systems

What does “Dry and Wet Systems” mean?

Well, the simplest rainwater harvesting systems are usually non-pressurized systems (like rain barrels) where the pipes run from rain gutters into a water storage tank. The “Dry systems” are known to be structures that do not hold any water in the pipes after it has stopped raining. This then does not create a breeding ground for mosquitoes and other insects.

“Wet Systems” are necessary when the pipes cannot be configured to run directly into the tanks. In places where the tanks are located some distance away from the collection point or where there are a series of tanks to serve a number of buildings, the pipes from the gutter then go underground and back up through a riser that leads the water into the tanks. These systems are often pressurized so the long-distance pipes do not retain stagnant water.

What are the design recommendations for rainwater harvesting?

A well-designed rainwater harvesting system ensures that the pipes and all the other openings are insect-proof, especially in wet systems. Wire mesh screen covers on all the tank inlets will help to prevent debris from entering the tank. The collection surfaces (mainly the roofs) should be made of non-toxic materials. Avoid lead-based paints and membranes. The tanks should also be made of non-toxic and noncorrosive materials.

Of course, care should be taken to ensure that the tank’s outlet taps or draw-off pipes are at least 10cm above the tank’s floor. This is to avoid drawing out any sludge that may have been collected in the water supply. Although most systems have a sump pump and washout pipe to remove the sludge, it is recommended to do regular cleaning of the inside surfaces of the tank. This is recommended for all systems.


Do I need to clean my gutters regularly?

In addition, all catchments should be kept clean of accumulations of dirt, moss, lichen and other debris. Tree branches that overhang those catchment surfaces should be trimmed back. Regular cleaning of gutters, tank inlets and screens are recommended. An annual tank inspection is necessary for the tank to function properly. The water in the tank should also be tested periodically so that you can monitor the water’s quality.

What are the different types of rainwater harvesting that we get?

Water Butt

This is the most basic form of rainwater harvesting systems, the garden water butt. Water is collected in a container from drain pipes and/or natural rainfall. This water is mainly used for the watering of your garden plants. People with a decent size garden will see a reduction in the amount of water used from the main water supply. You can pair the water tank with a rainwater filter so to further improve the quality of the harvested rainwater.

Direct-Pumped (Submersible)

This system is one of the most common types of professional rainwater harvesting systems. Domestic properties usually prefer this system, and it is generally the easiest to install. The pump is located within the underground tank and the harvested water is pumped directly to the water storage tanks.

If the tank should be in any danger of running dry, a small amount of water from the mainline is fed to the tank in order to maintain the water supply. For commercial uses, such systems tend to be a dual pump arrangement (duty standby).

Direct-Pumped (Suction)

With this system, there are a few differences. For one, the pump is not located in the tank but instead is located within a control unit in the house (e.g. a utility room). The control unit also deals with the backup from the main water line, so there is no need to send the main water to the storage tank.

rainwater harvesting systems

Indirect Gravity

This type of rainwater harvesting system differs from the rest. The harvested water is first pumped into a high-level tank (header tank). It then allows the water to be supplied to the outlets through gravity alone. With this arrangement, the pump only has to work when the header tank needs to be filled. The main water line is fed directly to the header tank, not into the main water storage tank.

Indirect Pumped

This system is very similar to the above one, except the internal tank can be at any level in the building, meaning it does not rely on gravity to supply water to the outlets. A booster pump set is instead used to provide a pressurized supply of water.

This system benefits of not having to feed main back-up water to the underground tank. It also offers great flexibility as the booster pumps can be made to suit the flow and pressure requirements of the building.

Gravity Only

Well, in some situations it may be possible to have a system that only functions through gravity, requiring no pump. In requiring no pump, the system does not use any energy. With this system, rainwater is collected from a part of the roof where the gutters are situated above the filter and the water storage tank. In turn, this is all situated above all the outlets.

This system is ONLY ever possible if the water storage tank is located below the level of gutters, yet is higher than the outlets that supply the water. The only power used in this system is gravity that is needed to feed the collected filtered water to various parts of the house to be used. We also call this system an ultra-energy-efficient option to harvest rainwater.

What are the advantages of a rainwater harvesting system?

  • Easy to maintain
  • Reduces municipal water bills
  • It is suitable for Irrigation
  • It reduces the demand for Groundwater

Now that you know more about the different rainwater harvesting systems available in South Africa, it will be easier to make your decision on whether you should invest in a Home tank or not. You can read more about our rainwater tanks in our blog https://www.aquadam.co.za/rainwater-tank-steps-before-beginning-your-installation/