Sea water quality

I’ve mentioned here and there in these pages that Durban has lost the internationally recognised Blue Flag grading on its beaches. The surprising part, for me, was that the city decided not to reapply, but to introduce its own grading standards. The whole thing is pretty complicated and I’m grateful to Tony Carnie’s article in the Mercury of September 1, 2008, for shedding a bit of light on the subject.

What’s at issue is how to measure the levels of faecal contamination in the sea water off our beaches and how to determine what the unsafe level is. There are many organisms that could pose a threat to bathers but the city has chosen to follow World Health Organisation (WHO) recommendations that tests are done to determine the levels of e.coli and enterococci in the water. These two organisms are used as indicators and the thought is that, if you count how many there are, you can assess how many other baddies are present.

There doesn’t seem to be much scientific objection to this way of going about things but the arguments start when it comes to deciding what the acceptable levels of e.coli and enterococci in the water are. The WHO says that seawater can be classed as excellent in quality if it contains less than 40 units of enterococci per 100ml of sea water. The standard for excellent water quality decided on by Durban is that it should have less than 100 units of enterococci per 100ml.

The WHO says that seawater should be classed as poor if the it contains more than 500 units of enterococci per 100ml which, they say, gives swimmers a more than 10% chance of contracting gastroenteritis. Durban has defined poor quality water as that which contains over 2000 units of enterococci per 100ml of sea water. Durban’s standards do not seem consistent with the WHO ones, and that that’s where the arguments start.

The city’s water and waste chief Neil McLeod argues that enterococci flourishes in warmer tropical waters and that you’d get more of them in the seas off Durban, without a corresponding increase in the quantity of other harmful organisms. Scientific opinion seems spilt on this matter leaving at least some room for doubt either way. Durban’s response seems to be less cautious than in other locations, such as in New South Wales in Australia. The state has beaches with cold water and beaches with warmer water but has apparently decided to adopt the WHO standards across the board. This will be until it is proved whether warmer water with increased levels of enterococci is really as safe as colder water with lower levels.

Waiting until there’s proof! Now, there’s a novel idea.


Leave a Comment