• Water monitoring is essential in ensuring a supply of clean water.Young woman drinking water. Woman With Water Glass. image by Monika 3 Steps Ahead from Fotolia.com
  
  There are a number of scientific methods used in determining the overall health of a given body of water. To avoid generating erroneous data, the tests should be carried out by suitably trained people using suitably calibrated equipment. After they are taken, samples should be tested as soon as practically possible.
  
  

pH

• The pH of a sample refers to its relative concentration of hydrogen ions. It is a measurement of the alkalinity or acidity of the water. The pH affects the solubility and availability of nutrients in the water and can be measured in three ways. The simplest and least expensive is to use pH indicator paper, but this is also the least accurate as it requires the tester to subjectively assess the resulting colour. Liquid colorimetric indicators also change color according to the water sample's pH. The most accurate method is to use an electrometric pH measurement meter. This is a pocket-size device that gives readings which are accurate within a range of 0.1 pH units.
  
  

Dissolved Oxygen

• The concentration of dissolved oxygen in a water body is essential to the survival of aquatic life. Cooler waters can be expected to have a higher concentration of dissolved oxygen than warmer waters. Dissolved oxygen is measured in milligrams per liter (mg/L) and there are two main methods used in obtaining these measurements. The Winkler method involves adding three chemical reagents to the water sample in the field. This is then titrated with sodium thiosulphate solution to determine the dissolved oxygen concentration. The electrometric method uses membrane electrodes attached to an electrically powered meter. The electrodes are immersed in the water sample and a reading taken.
  
  

Conductivity

• The ability of a water sample to conduct electricity is an indirect measurement of ion concentration. Conductivity is measured in microsiemens per centimeter (uS/cm) and is tested using a conductivity meter. This consists of a conductivity cell and two rigidly attached electrodes. The conductivity cell is immersed in the water sample and the meter reading is noted. A sample's conductivity should be measured immediately as its conductivity will change with storage.
  
  

Temperature

• The temperature of a water sample is expressed in degrees Celsius (C). How warm or cool a body of water is directly influences the amount of available dissolved oxygen. Temperature measurements must be taken immediately after the water sample is obtained. It is measured using a glass thermometer that is filled with either alcohol/toluene or mercury.