A water body's chemistry is critical to the life it sustains - changes in this chemistry can greatly affect the diversity in the water's ecosystems. There are many methods and tools available to allow us to monitor rivers, lakes etc and assess the impact of changes in the chemistry which are often due to human activity.

When taking samples of water for testing bear in mind that the substances which you are testing for are often in very low concentrations. Care must be taken as even a small amount of contamination of the sample will greatly affect your results. The sampling container used must not contain any trace of the substance you will be testing for and must be of suitable material that will not effect the substances it will contain. When taking samples for bacterial test sterile sample bottles must be used. Water samples should always be tested as soon as possible to minimise the changes that take place when the water is removed from the main water body.

Water dissolves substances it makes contact with and picks up dust from the air. It also supports photosynthetic life and often is polluted with man-made waste - all of these factors affect the waters pH level. Waters ability to buffer pH changes is essential to aquatic life. Generally, the abundance of living organisms will greatly diminish at pH levels greater than 9 or less than 5.

Samples should be tested within about two hours - the sooner the better as biological activity and gases lost can change the pH.

Test Strips - Simply dip a test strip into your sample. Then compare the colour change to a colour chart to give a pH level. This method is not very accurate but is quick and inexpensive - fine for when only an indication of pH is needed. Strips can be unreliable in water with low buffering potential or water containing substances which will interfere with the reaction on the strips.

Electronic Meters - These meters give much more accurate results than test strips by measuring the pH with an electrode(s). Although they do require some maintenance, they will give quick, accurate and easy to read results. Before testing ensure that the electrodes have been stored in a suitable solution and calibrated using a buffer solution. Choose a buffer solution around the pH levels you are likely to be reading. Temperature will affect pH and is measured and then compensated for in most meters.

Fish, invertebrates, plants and aerobic bacteria all require oxygen for respiration. Dissolved oxygen (DO) is mainly from the atmosphere, dissolving at the surface and being distributed by currents. Algae and aquatic plants also add to DO through photosynthesis. Build up of organic waste is one of the main factors to effect oxygen levels in our water systems. As the organic matter is decomposed oxygen is consumed -depletion of DO causes major shifts in the abundance of certain types of aquatic life. 5-6 ppm is usually required to support a diversity of life in the water.

Temperature, pressure and salinity affect the capacity for dissolved oxygen in water. The ratio of the capacity to the actual content of DO in the water gives a percentage saturation - a good indication of water quality.

There are specific and combination meters available to take DO readings - usually using an electrode. If taking a sample from below the surface waters test immediately or seal in a container with no air to minimise the addition of oxygen after the sample has been taken. Calibration is needed with these meters using a 0% oxygen solution.

Testing conductivity provides an estimation of the level of dissolved ionic substances in the water. Low values can indicate high quality oligotrophic (low nutrient) water and high values in eutrophic water nutrients (often due to fertilizers) are in abundance. Sudden changes to conductivity can indicate a new pollution source or spillage in the water system. Meters which measure conductivity use electrodes which must carefully maintained and calibrated with suitable conductivity solution.

Measuring the oxidation/reduction potential of water indicates it's tendency to accept/transfer electrons. Certain important biological processes can only occur in water within specific ORP values. ORP is affected by anaerobic biodegradation (such as in the eutrophication of a pond after being overly polluted with fertilizers) and therefore a good indication of a pollution source in an area.

Above are some of the main variables tested when water sampling. Other variables can include carbon dioxide levels, alkalinity and hardness. These can also be measured using test strips or chemical test kits which may not give the most accurate results but can give a good indication of levels.

You can also measure for specific substances which affect these levels such as measuring calcium for hardness. Photometers specific to an ion (e.g. calcium) measure the colour change when a water sample is reacted with a specific reagent. The colour change is measured and calculated to give the concentration of the substance.