The City of Cape Town’s Scientific Services Branch has detected unusual levels of algae have been detected in the water of Newlands Upper and Molteno reservoirs. According to the City, these algae pose no medical risk to the public but create a nuisance by clogging supply pipes, resulting in some consumers experiencing low water pressure. Consumers experiencing low water pressure have been advised to clean out the filters in their plumbing systems.

To reduce the effects of the algae on the distribution system, the City is diverting water from alternative supply systems. As soon as it is able to lower the reservoirs at Newlands Upper and Molteno, it will clear the algal growth. In order to prevent a recurrence of the problem, steps will be taken in the treatment process to raise the pH level of the water being fed into the open reservoirs. This will pose no health danger as treatment levels will meet the national SANS 241 standard for drinking water quality.

The procedure to empty the reservoirs according to the city requires significant resources and careful logistical planning. It is also weather dependent as the reservoirs play a vital role in balancing the supply and demand, and cannot be removed from service during periods of hot weather when the demand for water increases. It is believed the algae bloomed as a result of the change in the nature of the treated water together with the long spell of hot weather and the presence of sunlight in the only two open reservoirs in the system.

A national shortage of carbon dioxide, which is used in the stabilisation process of water treatment in the Cape, has further contributed to the problem. As only partial stabilisation can take place, the pH level of the water drops to a slightly lower level than normal in the reservoirs. It is also believed that this created an environment to support the algae.

The City says every effort is being made to rectify the situation as soon as possible.