pH: Many freshwater organisms have specific pH preferences and tolerances.

pH - Broad range kits: This type of kit is my favourite and the one that gets most use, more so than an electronic pH meter. Very often all I wish to know is a rough idea of the acidity or alkalinity and this sort of kit does it well with clear colours for each pH. It's compact and very quick to do at pond/stream side to assess for this kit pH 4-10 to nearest unit. Fill the water to the 10 ml level, add four drops of indicator and check colour against the bottom row on box. (The pots of chemicals shown aren't needed, these are buffers for aquarists to adjust aquarium pH.) Maker 'Waterlife'. Indicator sufficient for ca. 150 tests. The colour range for their narrow range kit pH 6.6-7.8 is along top of box.

pH - Narrow range kits: These can narrow down the pH but only perhaps to the nearest 0.4 - 0.6 rather than the optimistic 0.2 of the scales as the colour changes can be subtle. If accuracy better than ca. 0.5 is required this is where a pH meter would be better. This type of kit can only be used of course when it is known from a broader measurement that the pH lies in the kit's range. Maker 'Aquarium Pharmaceuticals'. pH 6.0 - 7.6. 250 tests. ca. £4.

In the author's opinion the above two aqueous kits give easier to interpret colours than the rolls of broad / narrow range pH paper familiar from school labs. The colours often seem to fade on these papers with storage and colours weak. Although there are modern small plasticised strips with bonded indicators for pH measurement and a wide range of other tests, but these aren't always available outside of the lab. suppliers and can be expensive.

Water hardness: Some organisms require calcium for their shells and exoskeletons.

The kit above is an example of the colorometric tests for either total water hardness (calcium and magnesium) or calcium. The number of drops of the final reagent required to change the colour of the sample from red to blue are counted. The number of drops x10 gives, in this case total hardness, in ppm. This kit and nitrate one below are more expensive than pH kits at ca. £7 but would probably be used less regularly for a given water body. Maker of above kit 'Aquarium Pharmaceuticals'.

Nitrate: Nitrate is the end product of the aerobic degradation of organic and inorganic nitrogen compounds present in water. Fertilizer run off from surrounding land can also influence the nitrate levels. The nitrate content can provide an indication of the level of pollution, which in turn will affect the occurrence of organisms sensitive to or tolerant of such pollution levels. In general, nitrate concentrations from 25 - 100 mg / l or more indicate increasing levels of pollution.

The nitrate test kit above is a typical maker's example with three reagents and pot of 'powder' with spatula. After completing the test sequence the colour after 10 minutes is compared with that on scale on the box for nitrate concentration. Maker 'TetraWerke' ca £9-50 for 50 tests.

Electronic pH meters: It's worth comparing specs of models before purchase; some of the cheapest may have no temperature compensation or may resolve to two decimal places when its accuracy is 0.2. The model shown does have an accuracy of 0.02 but on reflection was overkill for casual studies, a one decimal place model would have been sufficient. The cheaper kits don't always come supplied with two calibration solutions as here (although these small pots will require replacement). I haven't found this design as practical as the shorter more pocketable designs.

Errors are more likely to creep into the often more casual and occasional studies the enthusiast may make cf. a lab's studies where an electrode will be correctly stored and invariably the calibration checked before each study. The hobbyist's meters may be left for some time and less than ideally stored. To demonstrate the potential inaccuracies, I measured a known calibration solution after a few months storage without performing the maker's recommended 4h reactivation procedure. The stabilised reading was 0.4 too low.  

Conductivity: The electrical conductivity of water provides a measure of the total concentration of dissolved ions present and hence provides a general indication of the inorganic nutrient concentration of a water body.

The meter right is a typical model and very portable. Such meters, as did the author's, do not always come with a calibration solution and may give the impression that they are accurate straight out of the box. Not necessarily so, if the author's example is typical as it was reading 20% low before calibration.

Unlike pH meters, however, which typically have thin glass membranes which can change property with age and storage, the conductivity meters are measuring conductivity between two metal probes so are a lot more robust and less likely to change. After the initial calibration of the author's example it has remained fairly accurate with only occasional need for adjustment over nine years of intermittent use and storage.

A conductivity measurement of an unfamiliar water body is useful before pH measurements as it can show if it's of low ionic strength and thus potentially 'weakly buffered'. For such samples the pH can shift just by the act of measuring the pH so for more detailed projects studying such water bodies needs particular care in choice of equipment and measurement (as do accurate pH measurements of rainwater).

A  temperature compensated meter is worthwhile as conductivity is strongly temperature dependent. An auto shut off model is also useful. Waters with high salinity may need a meter with higher range. Make / model shown, Hanna DIST WP3, range 0-1990 µS/cm. Resolution 10µS, automatic temp. compensation. ca £53 nine years ago, cheaper nowadays.