Gardens, pools, rainwater tanks and grey water


Where houses have gardens these regularly consume as much as 40 to 60% of all the water used in the home. This is treated, drinkable water (that costs money to purify) and we need to think carefully about using it in the garden. We can be more efficient by watering during the coolest part of the day, using drip irrigation systems, composting regularly and adding mulch to our gardens. Some plants suited to growing in Cape Town (indigenous endemics) do not require watering at all, except during establishment.

In terms of the City’s new Water by-law gardens may not be watered using potable water, between the hours of 10:00 and 16:00. Where a hose pipe is used to water a garden from a potable water source, a controlling device, such as a sprayer must be attached to the hose end. (Water By-law Schedule 2, Water Demand Management).

Colourful indigenous and waterwise plants for our gardens

The Cape Peninsula has more plant species (2 256) than the whole of the British Isles (1 492). These indigenous plants – fynbos – have adapted over thousands of years to the local weather and soils and commonly have small, grey, waxy or hairy leaves to withstand the hot, dry summers. Indigenous plants are best suited to our gardens and require little if any maintenance and watering. An established waterwise garden may also add value to your property. The more waterwise you make your garden from the start, the easier and cheaper it will be to keep it beautiful. Once you have decided to make your garden more waterwise, discuss the options with your local nursery, or see City pamphlet “Creating a water efficient garden”.

If you must have a lawn, replace Kikuyu grass with indigenous drought-resistant grass, such as Buffalo grass (Stenotaphrum secundatum) and Fyn (Fine) kweek . These require half the amount of water and are low in maintenance. The lawns at Kirstenbosch Gardens (using indigenous grass species) are only watered once a week at night for three months of the year (during summer). Otherwise, these lawns rely on rain to survive and manage well.

Swimming pools

It takes 32,5 billion litres of water to fill the estimated 650 00 swimming pools in South Africa. The Western Cape has about 91 000 of these swimming pools. During hot weather, pool levels naturally drop 0,5 cm to 1 cm a day. Pool covers reduce evaporation by up to 90%, saving the water you would use to top up your pool levels. Plastic for pool covers costs approximately R40,00 to R50,00 a square metre. Sophisticated automatic roll-up stations and related accessories will cost more than R2 000,00. The more you need to top up your pool, the higher your bill will be.

Leaking pools can result in unnecessary water loss. Look for cracks inside the pool or an area of abnormally green grass. Better still, record how often you need to top-up your pool (this will be more regularly in summer). If the level of your pool drops by more than 5 cm to 6 cm a week, you probably have a leak.

In terms of the City’s new Water By-law automatic top up systems using a float valve fed from a potable water source to supply swimming pools and garden ponds is not allowed (Water By-law Schedule 2, Water Demand Management).

Boreholes and well points

A well point is normally an installation with a pump mounted at ground level, which draws up underground water via a suction pipe, from a depth not exceeding 8-10 metres. A shallow borehole has a depth of about 30 metres. Deep boreholes can have depths of 100 metres or more. Installing a borehole is very costly and should be fully researched beforehand. Groundwater may not be ideal for irrigating plants.

Groundwater plays an important role in the environment. During dry periods, groundwater recharges rivers when their flow is low. During wet periods, the opposite occurs; the rivers and surface drainage recharge the ground water. To ensure that borehole water is not polluted or overexploited, the amount of groundwater that is extracted needs to be monitored. That is why the Municipality requires all boreholes to be registered.

Rainwater tanks

While it is illegal to connect a rainwater tank to the drinkable water supply system, installing a rainwater tank for your washing, cleaning, watering or topping up pool water may be worth considering. Rainwater tanks may also be plumbed to feed toilet cisterns and so reduce the considerable amount of water used daily for flushing.

Use of rainwater tanks in summer rainfall areas can be more beneficial than those used in winter rainfall areas. However a 5 000 litre tank used primarily for flushing the toilet in winter rainfall areas could save up to 15% annually. This is using runoff from a 80 m2 roof and assumimng an average or above-average rainfall pattern.

Rainwater tanks hold different amounts of water: 200 litres, 500 litres, 1 000 litres 1 500 litres, 2 500 litres, 5 000 litres and 10 000 litres. Due to their relatively large size, a large area is needed for installation. To save space, choose a tank that is vertical and not horizontal. Placing the rainwater tank in the shade will help to keep the water as cool as possible. It must be borne in mind that a tank constructed of translucent material, will cause algae to grow in the water, if exposed to sunlight.

A 1 000 litre tank appears to be the most economical – and popular.

The black and white of grey water

Grey water comes from water used in the house for bathing, washing and cleaning. A grey water system will take this used water and transfer it to a garden watering system. The size and angle of the pipes that divert washing machine water is important. Filters, valves and a reservoir (for storage) are also necessary.

Laundry water with detergents containing phosphates is nutritious and may encourage plant growth. However, many washing-up liquids contain surfactant that is bad for our garden. Grey water from the kitchen should not be used to water the garden.

Grey water may not always be safe. You will need to know that you can safely monitor what is entering the water and manage the system properly. For health reasons, do not use grey water to water your vegetables, herbs or fruit that you intend eating. When using grey water in your garden, it is important that the water droplets are large and the spray is low so that the grey water does not travel to other areas.

This water must not be sprayed or sprinkled on your lawn on windy days. It is best to reuse this water using a drip system that drops the water directly onto plant roots. An even better grey water drip system uses piping under the ground. Take care not to allow greywater onto surfaces that drain into the street as this will pollute the stormwater system which flows to our rivers and streams. These systems are costly but are available in Cape Town. Installing a grey water system is complex.

Research the process thoroughly and make sure you use a reputable company.


Green your garden

Get practical

Make your own grey-water recycler
How to save water in gardens - the scrooge bottle
Hydroponic bog garden (water recycling)
World's greenest water pump
Green solar-powered water barrel
Homemade water sprinkler

Other water topics

Case study: Mrs Zenzele tackles a leaking tap
Save water - fix your own dripping taps
Toilets - save water
Baths, showers, geysers, taps and washing machines

Go green home