Dam levels for Cape Town decline in heavy rainfall month (May)

Dam levels for Cape Town decline in heavy rainfall month (May)

Dam levels supplying Cape Town have declined over the past week by 0.6% to 53.9% of capacity.

In a month were Cape Town historically receives 117mm of rain on average, with 11.4 wet days, it seems like the city might need to prepare itself for another year of water scarcity. Water consumption for the week increased to 676 million litres a day. It is however, still too early to predict whether another drought will grip the Mother City, but the rainfall for 2020 so far has been lower than the historical average.

Compared to last year, the dam levels for the City of Cape Town was at 45.3% and the average dam level for the Western Cape in 2019 was 33.5%.

Major Dam statistics
• Voëlvlei dam – 51% full this week (2019: 55%. Last week: 51.7%)
• Bergriver Dam 65.4% full this week (2019: 67%. Last week: 66%).
• Theewaterskloof dam – 50.4% full this week (2019: 35%. Last week: 50.9%)

Berg River dam, July 2019 – Photo: Vondeling Wines / Twitter

Rainfall pattern of Cape Town, month by month

Rainfall pattern of Cape Town, month by month

Cape Town rainfall pattern.

Cape Town falls within a winter rainfall area, with June receiving the highest average rainfall of 143 mm in the month. January is the driest month, receiving a measly 24mm of rain on average. The total rainfall for Cape Town sits at 853mm per annum. 

Average rainfall pattern for Cape Town

How often does it rain in Cape Town?

August has the most rainfall days with 13.7 day of rain, while February typically has the least with 4.6 days per month on average.

Cape Town average monthly rainfall days

The rainfall pattern in the Cape Town area allows for much rainwater harvesting over the wet winter months. These wet months make it possible to store vast amount of rainwater. This stored water can be used for irrigation use over the dry summer months or to replace the municipal drinking water supply. 

Should enough rainwater be harvested and stored  over the wet winter months it is possible to go off-grid for several months. Over the rainy season excess water will be stored for use during the dryer months. In mid summer, depending on water use habits, some municipal water may be needed to supplement harvested rainwater. The degree to which municipal water would be needed to be supplemented will depend on the available roof area used for harvesting and the water tank storage capacity.

Do I need an RPZ valve?

Do I need an RPZ valve?

do i need an rpz valve

The City of Cape Town has passed a regulation that all homes be fitted with an RPZ valve (Reduced Pressure Zone – also known as a backflow preventer). This is required where an alternative water supply is delivered to your house or garden with a connection to a municipal water supply, and includes rainwater and groundwater systems.

An RPZ valve will prevent backflow from your rainwater or groundwater system from feeding into the City water supply. This could occur in the event that mains water pressure drops below that supplied by your alternative pumped supply.

These valves are installed above ground and positioned immediately after your municipal stopcock. An isolation valve must be fitted either side of the RPZ valve with a suitable strainer installed at the inlet.

Older systems may have been installed with a safety feature in place to prevent contamination of municipal water. However, the City of Cape Town will only accept installations where an SABS approved RPZ backflow preventor is fitted. Non-return valves are not an approved method of prevention.

City inspectors are visiting homes where an alternative water supply is feeding into the home. They are also going door to door in areas where there have been complaints of poor water quality.

Please contact us at info@capewatersolutions.co.za or call us on 0834555385 to fit the required SABS approved valve for you. Where you have one installed it will require annual servicing, and we can provide you with a reminder to have your RPZ serviced. This will ensure that you stay in compliance with your city requirements.

What to look for in a grey water system

What to look for in a grey water system
There are a number of factors to look for in a grey water system that will help in determining whether the system is correctly designed to provide safe use and ease of maintenance. The following general rules will help when you look for a grey water system:


Size of chamber:What to look for in a grey water system

This is where your wastewater is temporarily stored before being pumped to garden. The chamber should be as small as possible, around 50 – 100 litres. The idea is to pump out your grey water as soon as possible. Larger systems that store grey water build up anaerobic bacteria within a couple of hours resulting in associated foul smells. It is these ‘storage’ type systems that give grey water a bad name.

Type of pump:

Your pump should be low pressure. High pressure pumps atomise (mist) grey water resulting in harmful pathogens floating in the air that can be breathed in. A good system will have a low-pressure submersible pump inside the chamber that is virtually silent when on. External irrigation pumps should be avoided at all cost.


Grey water is to be dispersed to the garden using either drip pipe or a pyramid type sprayer where larger water particles – delivered by a low-pressure pump – fall to the ground. Grey water should never be pumped through a standard irrigation system that requires pressure to drive the sprayers. High pressure pumps atomise (mist) grey water resulting in harmful pathogens floating in the air that can be breathed in.


The better systems will have a filter basket (much like a pool filter basket) for larger particles and a membrane (type of carbon sponge) for smaller particles. In the case of drip irrigation, a further in-line filter is required so that the fine holes in the drip pipe do not become clogged.

Cleaning the system:

To avoid a smelly grey water system the filters should be washed weekly and the main chamber cleaned every 6-months. The membrane filter should also be replaced 6-monthly. For this reason, easy access to your system is important.


Another factor to look for is if the supplier can provide washing powder and cleaning detergent that are developed with the correct enzymes to digest nutrients and particles in the water. Use of the correct washing powders and cleaning detergents will help mitigate smells by reducing the build-up of anaerobic bacteria in the waste pipes and chamber.

What is the best grey water system

What is the best grey water system

There are distinctly 2-types of grey water systems; those that do not treat grey water and those that do treat grey water.

Grey water diversion system
Grey water diversion system

a) Systems that do not treat grey water are used for garden irrigation only. These are diversion systems where wastewater from baths, showers, basins (not kitchen sink) and washing machines is diverted to a partially submerged chamber. From here it is pumped to the garden automatically to either drip pipe or low-pressure sprayers. The filtration used in these systems is normally a basket type filter to remove larger particles.

b) Systems that do treat grey water are used for flushing toilets, laundry washing, pool top-up and garden irrigation. The treatment used in these systems would include digestion (of the grey water bacteria) and either UV-sterilisation or membrane filtration. Although these systems are more versatile the cost is usually far greater than the simple diversion system for garden irrigation. See Hydraloop and Aqualoop treatment systems.

2019 – Another drier than average year

2019 – Another drier than average year

Another drier than average year

The City of Cape Town has cautioned residents to keep an eye on consumption levels over the coming weeks. Water consumption for last week was up to 657 million litres/day, exceeding the current 650-million litres/day limit.
Dams supplying Cape Town are down 1,0% from the previous week sitting at 79,7% of storage capacity.
2019 has been another drier-than-average year, and it is important that Cape Town residents remain aware of their water use, especially as we approach the summer months.



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