One of the standard methods of looking at water quality is to sample a stream.
However a very low, or zero, bacteria result doesn’t mean the location is a safe source.
Below are three reasons why a low bacteriological sample value may not be providing good information:
Sample Not Truly Representative
The typical stream sample is 1 Litre.
Even a small stream is likely to have a flow of up to 500litres/min, thats 720,000 litres per day.
That means you are sampling 0.00014% of that days flow, hardly representative!
Changing Water Quality
Water Quality in a stream is not consistant, for example:
- Rainfall will wash dirt and faeces into the stream.
- Dry periods, with low flows, may concentrate any contamination
- Animals, birds, and humans live in the catchment and may use it for washing, and defacation.
For accurate testing extensive protocols need to be performed, for example:
- Proper preparation of sample bottles;
- Refrigerate samples during transport:
- Deliver to an accredited laboratory on day of collection;
For a full range of protocols see this Tasmanian Goverment document Community Water Samples
Without the correct protocols, which may be difficult in many developing countries, the may be very large.
The Value of Water Testing
The above problems do not mean that water testing shouldn’t be carried out.
Water Tests are valuable for:
- Comparing bacterial quality of different sources of water for a community.
- Providing Information on the types of natural chemicals in the water that can cause health concerns, for instance arsenic, and flouride.
- Identifying pollution from industrial processes and mining.
How To Achieve Safe Water
The best way to ensure safe drinking water is:
- Having a source water that is free of harmfull chemicals.
- Have a treatment system that reliably removes ALL bacteria from the water.
Disaster Aid Australia continue to install SkyHydrants, as they have proved highly effective at removing all bacteria from water.
This has reduced illness in serviced communities by more than 70%.