Cape Town

Catchment areas

Cape Town’s main catchment areas are the mountain fynbos areas located to the east and north-east of the city, including the Hottentots Holland, Riviersonderend, Wemmershoek, Wellington, and Porterville mountain ranges. Table Mountain is also a catchment area although these days it contributes less than 2% of Cape Town’s total water supply.

Mountain fynbos catchment areas

Rainfall is highest in these mountainous areas, often exceeding 2 000 mm per year. This is a significant amount considering that some parts of the city receive as little as 300 mm per year. Most rain falls during winter storms are caused by cold fronts. Moist air and clouds blown inland from the Atlantic are forced to rise over the mountains. This causes the air to cool and moisture to precipitate as rain and sometimes as hail or snow. The water drains into streams and rivers, and flows downhill towards the sea in rivers such as the Berg, Riviersonderend, Palmiet and Steenbras. Some of this water is captured and stored in dams that supply the Cape Town water system and the rest is returned to the rivers to sustain the river systems.

The pristine undeveloped nature of our catchment areas contributes to the excellent quality of the water we drink. However, Cape Town’s raw (untreated) water is tea-coloured from plant matter that is dissolved in the water, and is soft and acidic. This is corrected during the water treatment process.

Approximately 98% of our water comes from dams. For this reason, our catchment areas need to be protected. Poor agricultural practices or urban development within catchment areas can have a negative effect on the quality of our water sources.

Invasive alien plants consume more water than the indigenous fynbos and are a threat to our water resources. The Working for Water project helps to clear alien vegetation in our catchment areas and creates employment opportunities for local communities.

Groundwater
Most of our water is surface water (water collected from rivers and dams). However, approximately 2% of our drinking water comes from groundwater sources.

Examples of these:

• The area of Atlantis, which is supplied with water pumped from the Atlantis Aquifer. This is an underground water body that is formed between the sand grains of the sandy soil that occurs in the area. This water is pumped from boreholes at two well fields: one at Witzand near Atlantis and a smaller one near Silverstroom Strand.
• Water that is pumped from boreholes along the Lourens River in Somerset West
• Water that is sourced from the Albion Spring in Newlands

The growing demand for water

Until 1921, Cape Town was supplied exclusively with water from Table Mountain. However, as the city grew, this proved to be insufficient and water from further afield was sought. This led to the construction of the Steenbras dam above Gordon's Bay and a 63 km pipeline was needed to transfer the water to the city. Today, water is transferred from several other catchment areas, including those from the Berg, Riviersonderend and Palmiet rivers via an integrated supply system known as the Western Cape Water Supply System. This network consists of an intricate system of dams and pipelines managed either by the City of Cape Town or the National Department of Water and Sanitation.

Additional water sources will be required as the city continues to grow. The Berg River-Voëlvlei Augmentation Scheme scheme has been earmarked as the most suitable next augmentation scheme. The scheme involves the diversion of surplus winter water from the Berg River for storage in the Voëlvlei Dam and has an estimated yield of 23 million m 3 per annum. Additional future water sources being considered include:

• sea water desalination;
• water reclamation;
• groundwater from the Table Mountain Group Aquifer – a large aquifer running under the Cape Fold Mountains;
• diversion of the Lourens River; and
• diversion of water from the Upper Wit and Molenaars rivers.

Dams

Cape Town is supplied by 14 dams with a collective capacity of approximately 900 000 Ml (900 000 000 000 litres). Most of this capacity is provided by six large dams: the Theewaterskloof, Voëlvlei, Berg River, Wemmershoek, and the Steenbras Upper and Lower dams. The remaining dams are much smaller and only contribute 0.4% to total capacity. The three largest dams are owned or managed by the National Department of Water and Sanitation.

Until 1897, Cape Town relied on spring river water which usually reduced to a trickle in the summer months. This supply challenge changed with the construction of Cape Town’s first dam, the 954 Ml Woodhead Dam on Table Mountain. These days, the city has access to water storage of nearly 1 000 times greater capacity, provided by 14 dams, and is integrated into the wider Western Cape Supply System.

Water treatment

The quality of drinking water in Cape Town is of an extremely high standard. This is due to the quality of the treatment processes, and from the fact that most of the water consumed in Cape Town is abstracted from unpolluted mountain catchments and aquifers. Cape Town water complies with the stringent guidelines as stipulated in the South African National Standards (SANS 241:2015) for drinking water and has received multiple Blue Drop awards from the Department of Water and Sanitation for its water quality.

Our water treatment works

Cape Town has 12 treatment works, ranging in treatment capacity from 3 Ml per day, at Constantia Nek to 500 Ml per day at the state-of-the-art Faure Treatment Works. Collectively, these plants provide a treatment capacity of approximately 1 600 Ml per day. Prior to the introduction of water treatment, all water supplied was tea-coloured due to plant matter suspended in the water. However, more serious problems included the build-up of sediment in the pipelines, which caused blockages, and the water’s high acidity levels, which corroded pipelines and valves.

How is the water treated?

Treatment processes at the treatment plants vary slightly according to the plant and the type of raw water being treated. In general, the treatment processes involve the following steps:

Coagulation and flocculation: Chemicals including aluminium sulphate, ferric sulphate and sodium aluminate are added to the water. These substances cause water-borne particles to clump together to form bigger, heavier particles that are easier to remove from the water. The chemicals are removed from the water during the treatment process and do not remain in the final treated water. The high pH (alkalinity) levels of the water at this stage help to destroy any bacteria and viruses that may be present in the water.

Settlement (sedimentation): The particles are allowed to settle at the bottom of settlement tanks and are later removed as sludge. The sludge is then dried and removed to a waste disposal site.

Stabilisation: Lime and/or carbon dioxide gas is added to water to adjust the water pH levels and softness.

Disinfection: Chlorine is added to kill any pathogens. It is important that a small amount of residual chlorine remains in the final water, to keep it safe from the possible introduction of any pathogens while in the water distribution network.

Reservoirs

Cape Town is serviced by 25 bulk reservoirs and more than 100 smaller distribution reservoirs store treated drinking water before it is piped to homes and businesses.

Why are reservoirs important?

Reservoirs are an important part of any water reticulation system. Water is supplied to reservoirs at a fairly constant rate from the City’s water treatment plants. However, the amount of water needed to supply homes and businesses fluctuates throughout the day.

Demand peaks in the morning and the evening, but dips in the middle of the night when most people are asleep. This is a bit like rush hour for water. Reservoirs help the water reticulation system to cope with periods of peak demand. All reservoirs are built on hills in and around the city. Many are built approximately 110 meters above sea level to help create the right amount of pressure in our water pipes.

Cities in flat areas require water towers to help create water pressure. However, this is not necessary in Cape Town because of our conveniently located hills. Most reservoirs are enclosed. However, the historic Molteno and Newlands reservoirs are open.

Reticulation

Every day, approximately 880 000 Ml of treated, drinking water is distributed to nearly 650 000 consumers through a network of 94 pump stations, 26 large reservoirs, 103 smaller reservoirs and about 10 600 km of pipeline ranging from those big enough for two people to walk abreast to the standard domestic 15 mm or 20 mm connections.

Laid end-to-end, the pipes would reach Melbourne, Australia.

Every year, around 16 000 drinking water samples are drawn from approximately 300 designated sampling points and are laboratory tested to ensure compliance with stringent water quality standards.

Our wastewater network

Wastewater is piped to treatment facilities via a network of 9 200 km of pipeline and 385 pump stations. The city’s largest sewer pipeline is 1.8 m in diameter at its largest point.

Sewer pipes are generally larger than water pipes. Unlike water pipes, they are usually not pressurised and instead flow by gravity. The exception is “rising sewer mains”, which allow wastewater to be pumped uphill.

Non-drinking water network

A third type of pipeline is Cape Town’s non-drinking water network. This smaller network conveys treated wastewater or spring water to customers for irrigation or industrial use.

Pipe replacement programme

The City of Cape Town is actively pursuing a pipe replacement programme to replace ageing
pipelines in order to limit pipe bursts, water leaks and sewerage spills. Through this programme,
about 30 km of sewer and 40 km of water mains are replaced each year.

Sewer blockages

A major challenge is the excessively high number of sewer blockages currently being experienced. On average, the City attends to nearly 300 sewer blockages every day.

Blocked or overflowing sewers are unpleasant, can cause health hazards, and are bad for the environment. The additional burden of clearing these blockages results in increased operational costs, which ultimately leads to higher service charges.

Water consumption

The City of Cape Town provides water and sanitation services to more than 3.74 million people (2011 Census) via water and sewer connections that supply nearly 650 000 properties.

However, Cape Town is growing rapidly and this figure increases every year due to population growth and migration to the city. Each year, on average, the Water and Sanitation Department provides connections to 8 500 new customers.

Our customers include:

• approximately 156 000 informal households in 204 informal settlements throughout the city, which are serviced by approximately 11 000 communal taps and 52 000 toilets;
• approximately 600 000 domestic consumers;
• approximately 13 000 commercial consumers;
• approximately 6 500 housing complexes and blocks of flats;
• close to 4 500 industrial consumers; and
• two other municipalities: the City provides treated drinking water to Drakenstein (Paarl) and Winelands (Stellenbosch) municipalities.

All water consumption from formal properties in Cape Town is metered and consumers are billed according to how much water is used. All properties are connected to the water network via a water meter, which is usually installed in a small chamber beneath the pavement directly outside the property. The meter is read monthly by a team of water meter readers.

Consumption varies greatly across suburbs. Most houses (properties on the Domestic full tariff) consume between 200 and 600 litres per day (6 and 18 kl per month). Above 1 000 litres per day (30 kl per month) can be considered as high consumption. Houses with large gardens and swimming pools usually consume more water, while flats and houses with smaller gardens generally consume less. Low-income households consume much less water, unless there are plumbing leaks on the property.

Average domestic consumption calculated over a 12 month period is 660 litres per day (20 kl per month) for houses (Domestic full tariff) and 460 litres per day (14 kl per month) for flats and complexes (Domestic cluster tariff).

Wastewater treatment

The City of Cape Town operates 17 wastewater treatment works (sewerage works) and six smaller facilities. Wastewater undergoes a closely monitored treatment process before being safely discharged into rivers, canals, vleis, underground water bodies called aquifers, or the sea.

Cape Town’s wastewater treatment works use different processes to clean the water. However, most treatment works include the following treatment steps:

• Pre-treatment and screening to remove large foreign matter such as rags, paper, plastic, leaves, etc.
• Filtration of grit, sand, small stones and broken glass. It is important to remove these at an early stage so that they don’t cause damage to pumps and other equipment later on in the treatment process.
• Primary sedimentation in order to remove solids, which are treated separately as sludge. Fats, greases and oils are also removed in this stage.
• Secondary treatment processes used in Cape Town works include activated sludge, bio-filtration and rotating biological contactors. Oxidation ponds are also used in some small rural works. In this treatment phase, microscopic organisms are used to process the wastewater to remove organic matter and various chemicals such as ammonia, nitrogen and phosphorous.
• Disinfection using chlorine, ozone or ultraviolet light to kill bacteria, viruses and other pathogens. In some works, the final treated effluent is allowed to remain in maturation ponds, which improves the quality further before it is discharged.

The quality of treated wastewater is monitored on a weekly basis to ensure compliance with licensing conditions and national standards. Treated wastewater is re-used for irrigation or industrial use in the city.

Infrastructure investment

The City is continually investing in its wastewater treatment works to improve the quality of our treated effluent and keep pace with our rapidly growing city. Key investments include a R150 million, six-year upgrade to the Athlone works which will increase its capacity and improve the quality of treated effluent discharged into the Black River. An extensive plant upgrade is also in progress at the Bellville treatment plant.

The city’s newest treatment works opened in Fisantekraal in 2012. It uses state-of-the-art ultraviolet disinfection and is geared as a ‘zero discharge’ plant, as the treated water is piped to customers for irrigation purposes.

Marine outfalls

The City of Cape Town operates three marine outfalls that discharge wastewater deep underwater far into the sea where the effluent is safely dispersed. All three consist of the following components:

• A pre-treatment works where sand and grit is removed and the effluent is screened to remove plastic, paper, rags and any other foreign material
• A pump station
• An underwater pipeline designed to withstand wave actions and possible damage from ship anchors
• A diffuser at the end of the pipeline that helps to disperse the waste

Why do we need marine outfalls?

While many people may feel uncomfortable about discharging largely untreated wastewater into the sea, it is important to consider that marine outfalls are carefully designed to safely disperse wastewater deep underwater far from the shore. They are located in areas where ocean currents help to disperse and carry the effluent away from the coast. The enormous volume of the sea helps to dilute the waste to nearly undetectable concentrations, and bacteria and pathogens die off while mixing with the sea water.

Our marine outfalls generally serve densely urbanised areas where the establishment of a land-based treatment works would be difficult due to limited availability of suitable land.

Marine outfalls in Cape Town

Cape Town’s first marine outfall was constructed at Mouille Point as far back as 1895, and four outfalls have since been built in the area. The original outfall was replaced by a 180 metre pipeline in 1927.

The current one, which serves the greater CBD from Woodstock to Bantry Bay, is 1 700 m long and discharges 28 m below sea level. It was urgently constructed and commissioned in 1993 in order to replace the previous outfall (built in 1985) which had been damaged by winter storms in 1989. Camps Bay outfall was commissioned in 1977 in order to replace an inadequate previous outfall. Hout Bay outfall was constructed in 1991 and became operational in 1993 after the completion of the pre-treatment works in 1992.

A fourth marine sewer outfall is located on Robben Island and is managed by the Department of Public Works. A small, land-based treatment works is planned to help cope with the increasing number of visitors to the island. This will treat the wastewater before it is pumped out to sea in the existing outfall pipe.

Treated effluent

Treated effluent, or recycled water, is wastewater that has been treated at wastewater treatment (or sewerage) works and then piped via a separate network of pipes to various consumers. In Cape Town, this water is not used as drinking water but for irrigation and industrial purposes.

Recycling our water

On average, approximately 3 300 m3 of this water is consumed every day. In this way, Cape Town recycles 5% of all water used. This water is much cheaper than drinking water and the City of Cape Town actively promotes its use in order to conserve Cape Town’s limited drinking water
supply.

There are more than 160 treated effluent consumers in the city including schools, sports clubs, golf courses, farms, industry and commercial developments with large water features. The City also uses this water for irrigating parks and the flower beds along Cape Town’s Integrated Rapid Transport (IRT) routes.