This response to a DEWPoint helpdesk enquiry draws on the literature to answer the following questions:
Do we have any reasonably robust way of estimating the probability of harm to service users from a 10 faecal coliforms/100 ml count? Or indeed any count between 0 and 10. (For Malawi, we would pose the same question at 50 per 100 ml and 10-50 per 100 ml).
Do we have any study linking the performance on microbiological tests on commissioning a water source to microbiological results at given periods after that date?
If we were to wish to, are we able link health outcome data to microbiological results? (The same question could be asked of non-microbiological contaminants).
We are interested in any risk exposure we incur by adopting standards on individual contaminants which are more lax than the national government’s. We understand why we may wish to use different standards, and perhaps advocate for their adoption, but perhaps where we do, the compliance risk should be assessed and documented.
This report was produced by DEW Point, a Resource Centre for Environment, Water and Sanitation, that was funded by DFID and managed by a consortium of companies led by Harewelle International Limited. The Resource Centre closed in 2012.
Tyrrel, S. Water quality standards and microbiological contamination. February 2011. DEW Point, Blisworth, UK (2011) 13 pp.