Cryptosporidium in water supplies
FR/R0005
Revised September 2006
Summary
Cryptosporidium is a parasite which can produce an unpleasant gastric illness known as cryptosporidiosis. The parasite is transmitted in an encysted form known as an oocyst. At the present time there is nothing to treat cryptosporidiosis other than the body's defence systems. Cryptosporidiosis can, therefore, be a serious problem in people with weak immune systems such as young children, the elderly, people on cytotoxic drugs and those suffering from AIDS. Cryptosporidium is the third leading cause of non-viral gastro-intestinal illness in the UK

There are a number of different species and strains of the parasite, but those which can infect human beings are also capable of infecting some animals, and vice versa.

Cryptosporidium is frequently waterborne in natural waters and infections have occurred from drinking contaminated water supplies. However, there are many other possible sources of infection such as zoonosis (animal-person contact), contaminated food and contaminated swimming pools and other recreational waters (rivers and lakes), or foreign travel.

A well-operated drinking water treatment plant can physically remove over 99.99% of oocysts from an affected raw water. Traditional processes such as coagulation, clarification and filtration remain the best defence against this parasite entering supplies.

The effectiveness of chemical disinfectants is very limited as revealed by the available measures of oocyst viability. However there are indications that UV light may be effective.

In the UK there are regulations to control the risk of pathogens getting into the drinking water supply. There are also additional regulations which are aimed specifically at the control of Cryptosporidium oocysts in the water supply which specify that there must be no more than 1 oocyst per 10 litres of water, regardless of whether the oocyst is viable or not. This regulation is intended as an operational standard for the performance of treatment works. The rationale is to ensure that the processes of physical removal are continuously capable of removing oocysts when challenged with their presence in raw water sources.

Copies of this report are available from the Foundation, price £15.00, less 20% to FWR members.