Criteria table
"Cutpoints" separate the water quality into four classes using the
90th
percentile.
Please note that these classes are based on only a few water quality criteria,
and that the algorithm classifies a whole quaternary drainage region
on the basis of as few as 5 samples for a minimum of just one station!
Also be aware that the algorithm classifies dams separately from the drainage region in which they occur.
Checking the original data is essential before drawing conclusions
about individual catchments or dams.
For example, coastal lakes may have a very high natural salinity.
| Class | definition |
|---|
| 0 | ideal water |
| I | safe water |
| II | short-term use |
| III | undrinkable |
Most variables have three cutpoints (and zero defining the minimum for Class 0),
except pH, which needs six cutpoints to define acid and base ranges.
Only one variable needs to be in a higher class for the whole classification to be bumped up
into that class.
Units are mg/litre except pH (-log [H+]) and EC (milliSiemens/m).
| Variable | Type | Cutpoint
1 | Cutpoint
2 | Cutpoint
3 | Cutpoint
4 | Cutpoint
5 | Cutpoint
6 |
| pH |
2 |
4 |
5 |
6 |
9 |
9.5 |
10 |
| F |
1 |
1 |
1.5 |
3.5 |
| NO3 |
1 |
6 |
10 |
20 |
| SO4 |
1 |
200 |
400 |
600 |
| Cl |
1 |
100 |
200 |
600 |
| Na |
1 |
100 |
200 |
400 |
| Mg |
1 |
30 |
70 |
100 |
| TDS |
1 |
450 |
1000 |
2450 |
| EC |
1 |
70 |
150 |
370 |
Table of concentration ranges used by
/prjws8/users/michael/aml/qatrivhtml.aml
to generate colour-coded maps of chemical status
of South African catchments.
[Chemical index page]
[IWQS home page]