When shopping for a back-up water tank, the choice of tank as well as its water supply system will be informed by, among other things, the water source. Tanks from locally available brands such as Jojo, Roto and Eco can either be filled using the municipal water supply, rainwater harvesting, or both as part of a fully integrated system. It can sound a bit technical, but we break it down for you. 

Municipal back-up tank

Municipal back-up systems include a tank that is connected to the municipal water supply. This fills up automatically when water is available from the tap, and if there is a water cut it supplies water to the home. Since the water comes directly from the tap, it should be clean and ready to drink. 

However, if you’re unsure about the quality of municipal water in your area, consider adding a post-tank water filter. This could be an under-sink or countertop filter for taps that provide drinking water. 

Alternatively, a whole-house filter could be installed outside, close to the tank and water pump, so that it filters all the water going into the house. This system would also have a pressure sensor, which recognises when municipal water gets cut, so that it can start pumping water into the house.

Rainwater harvesting tank

A rainwater harvesting system fills up automatically when it rains. While the water is free, this system requires piping and guttering to get rainwater from roof to tank. Without proper post-tank filtration, rainwater is suitable for washing, irrigation, toilet flushing, car washing, filling up a pool, and other similar uses. 

The tank system should also have a pre-filtration system that includes one or all three of the following: a mesh screen below the lid of the tank to keep out insects and debris, a rainhead fitted to the downpipe to direct leaves and debris away from the water flow before the water gets to the tank, and a first-flush rainwater diverter to flush away the initial water, which is likely to be the most contaminated. 

If the water is to be used for drinking, it is crucial to include an additional water filtration system for water coming out of the tank, like the aforementioned whole-house filter, since the system needs to be able to remove sediments, bacteria and other harmful substances. It is highly advisable to do this with the help of a qualified installer.

Fully integrated system

A fully integrated system uses both municipal and rainwater. It gets filled up to a predetermined level with municipal water, and the remaining space is available for rainwater. This tank would typically supply water for full domestic use, hence it requires a whole-house filtration system as well. This would also require a larger tank due to a certain level being constantly full of municipal water.

Choosing the right size for your household

Manufacturers typically quote South African per-person water consumption at 150 litres a day. Studies have put use on an average of 235l per day, well above the global average of 185l per person per day. 

However, these statistics include a country’s industrial water use as well as leakage. As per a fact check on the statistics, conducted by Africa Check, the actual amount of water used by individuals can be significantly lower, even down to 50l a day. 

That said, working on the 150l-per-person average quoted by tank manufacturers, one would calculate the number of people in a household to work out the ideal tank size. For example, a household of four people using 150l per person per day would require 600l a day. To cover for a potential water cut of three days, the household would require a minimum tank size of 1,800l.

To pump or twist

At its most basic, a tank only requires a simple tap to enable access to the water. If it contains municipal water, this is normally safe for drinking. However, if the tank is filled with rain-harvested water, it would need further filtration or sterilisation. 

Alternatively, an electric pump can be installed to create a pressurised system so that water can be pumped into the household. Pumps differ in power based on need, with higher-powered pumps better suited to larger households. It is important when buying a pump to ensure that one discusses their specific needs with the installer to ensure an appropriately powered pump is fitted for the household. DM/ML

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