The City of Cape Town wishes to inform residents that unusual levels of algae have been isolated and identified in the water of Newlands Upper and Molteno Reservoirs by the City’s Scientific Services Branch.

These algae pose no medical risk to public health as they are non-toxic genera, but do exhibit a high nuisance factor due to their filter-clogging characteristics. The dominant genus observed is Mougeotia. As a result some consumers are experiencing low pressure.

If uncharacteristic low water pressures are experienced, consumers are advised to clean out the filters in their plumbing systems. Residents with home filters are always encouraged to check and clean filtration systems regularly.

In order to reduce the effects of the algae in the distribution system, the supply system is being adjusted to minimise the flow of water through the two reservoirs by maximising alternative systems. This will reduce the areas of supply from Newlands Upper and Molteno Reservoirs until the City is able to lower the reservoir and clear it of the algal growth.

In order to reverse the effect of the water supporting the growth of the algae, steps will be taken in the treatment process to raise the pH of the water being fed to these open reservoirs. This will pose no health dangers as the all determinants will always be kept within the limits allowed in SANS 241, the national standard for drinking water quality.

The procedure to empty the reservoirs requires significant resources and careful logistical planning. It is also weather dependant as the reservoirs play a vital role in balancing the supply and demand and cannot be removed from service during these periods of hot weather and associated high water demands.

It is planned to drop the levels towards the end of the week and during the weekend, while demands in the respective areas are reduced, and then to remove as much of the algae as possible. Additional options to remove the algae are also being considered.

These algae can occur in very low numbers in reservoirs, as they are prevalent world-wide in clean waters with low nutrients and low pH. The algae have not been detected in the incoming water supplies. It is believed that these algae have 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 used in the stabilization process of water treatment in the Cape, has further contributed to the problem. As only partial stabilization can take place, the pH of the water drops to a slightly lower level than normal in the reservoirs and it is believed that this has created an environment that supports the algae.

The water levels in the reservoirs rise during the night when the demand in the area is low and falls during the day while the peak demands prevail. Both reservoirs are cleaned annually during low demand periods in winter.

The City wishes to apologise for any inconvenience that this situation has caused and wishes to assure the public that there is no health risk and that every effort is being made to rectify the situation as soon as possible.

Issued by: Integrated Strategic Communication and Branding Department, City of Cape Town and submitted by Liz Williamson : Claremont Cluster CPF Chairman


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