River water pH
There are two main ways to test the pH (degree of acidity or alkalinity) of river water.
The high-tech method uses a sensitive electronic probe attached to a digital display. The traditional method uses pH paper, which is like litmus paper but more specific.
Digital pH meters all come with instruction manuals, but the general method is similar across them all. They consist of a delicate probe (often glass) on the end of a handle. You dip the probe into the water and read off the pH via a digital display on the handle.
The meter may need to be calibrated first by dipping the probe into one or more specially produced fluids of known pH, and adjusting the display to read the correct value. Other meters come ‘ready-calibrated’ from the manufacturer.
Before use the probe should be washed very gently in pure distilled water and dried with a soft clean cloth to remove any impurities.
Collect a sample of water in a sterile container, lower the probe into the sample to the required depth (marked on the probe) and leave it there until the digital display gives a constant reading.
Digital meters give readings accurate to either +/-0.1 or +/- 0.01
The paper version of the test has many advantages for use in fieldwork. It doesn’t need batteries, there is no sensitive probe, its cheap and easy to use. No surprise then that it’s the method you are most likely to use for fieldwork.
Collect a sample of water in a sterile container, or a container well rinsed out with the same river water.
Tear a strip of pH paper off the reel and dip it into the water.
Remove it from the water, don’t shake it around or dry it, just hold it still while it changes colour.
Unlike litmus paper that changes colour all over, pH paper changes to show a pattern of different coloured lines. Compare the coloured lines showing on the paper to the guide chart supplied with the paper to determine the pH of the water.
In both cases remember to record the value straight away. Don’t rely on memory.
Repeating the test two or three times can help to eliminate errors and give you a more reliable average value.