Report No DWI0777
Cryptosporidium incidence in private water supplies and correlatory indicators
- The Department of the Environment's 'Cryptosporidium
in Water Supplies - National Research Programme' has carried out
extensive work on the detection, aetiology and removal of the organism.
One area that deserves further examination is the incidence of Cryptosporidium in private water supplies. This study has therefore tried to establish the extent to which Cryptosporidium occurs in private water supplies.
- Fifteen private water
sources in the Bradford and Craven local authorities' areas have been
sampled over a three month period for Cryptosporidium, Giardia
and potential indicators. All the supplies were considered to be
reasonably likely to contain faecal material, based on a sanitary
assessment of the catchment site and previous sampling results In order
to eliminate the possible effects of treatment on the incidence of Cryptosporidium
in private water supplies all samples in this study were taken prior to
treatment, where fitted and sampling was undertaken at times of
greatest precipitation. Cryptosporidium was found in twenty one
(14.00%) of the samples taken. This has ranged from no positive results
in some of the supplies to 40% positive in the most highly
contaminated. Nine of the fifteen supplies (60%) have been found to
contain Cryptosporidium during the survey period.
- The study also looked at other parameters of water quality to try and establish a link between them and the occurrence of Cryptosporidium. There was a statistically significant correlation to Cryptosporidium for faecal streptococci and Clostridium per fringens.
- There was no significant correlation between the detection of Cryptosporidium and coliform bacteria, either total or faecal, turbidity, conductivity or a sanitary assessment score.
- Twelve positive results for Giardia
cysts were found in a total of 150 samples (8%). This is lower than has
been found in North American raw water studies and may indicate a
difference in the background incidence between the two countries. Eight
of the supplies had positive samples for Giardia (53.3%), which
is close to the results found in a UK raw water survey (Gilmour et al.,
1991). All these supplies were also positive for Cryptosporidium.
- Further study is
required to explore the possibility of improving sanitary scoring
accuracy in order to obtain a statistically significant relationship
with Cryptosporidium perhaps allied to turbidity measurement. The extent of possible Cryptosporidium occurrence in lower risk supplies and at different times of the year also needs investigation.
- There was no evidence of Cryptosporidiosis in those consuming the water in any of the supplies.
Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.