Residents are advised that unusual levels of algae have been detected 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 but they do create a nuisance as they clog supply pipes. As a result, some consumers are experiencing low water pressure. The dominant genus observed is Mougeotia.
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 on the distribution system, water is being diverted from alternative supply systems. This will reduce the water 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 prevent a recurrence of the problem, steps will be taken in the treatment process to raise the pH-level of the water being fed to these 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 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 periods of hot weather and the associated high demand for water which arises.
Plans are underway to drop the reservoirs’ levels towards the end of the week and during the weekend, while demand in the respective areas is 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 water sources with low nutrients and low pH-levels. 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, 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 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 peak demand prevails. 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. Every effort is being made to rectify the situation as soon as possible.
