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Notes on water-quality criteria:
“Safe” or “acceptable” levels of E.Coli are the subject of much scientific and policy debate.
The International Blue Flag programme specifies an E.Coli single-sample limit of 250 cfu/100 ml.
Public Health specialist and Water Watch SA advisor Professor Edda Weimann, has this to say about the guidelines:
“National guidelines are applied for water quality without any proof that these levels are not harmful.
“This was chosen as a convenient threshold because certain precautions (clean rivers, clean stormwater, no outfalls) have to be implemented to achieve lower levels.
“If they would apply the 100cfu/100ml standard, most of our beaches would have to be closed on a regular basis. Other countries have implemented lower standards for E. coli to reduce possible health risks.”
Read her full comments here.
For example, the New Hampshire Department of Environmental Services specify that “E. coli levels at designated swimming beaches should not exceed 88 per 100 millilitre (mL) in any one sample, or exceed a three-sample geometric mean average over a 60-day period of 47/100mL”.