This free course, Understanding water quality, provided an introduction to studying. It described the main characteristics of natural water and how these may be altered by pollutants of various types. The course also outlined the key stages of treatment for water supply and for treating waste water in sewage treatment works.
In this course you have learned that:
- Pollution is a deterioration of water quality caused by human agencies that makes the water less suitable for use than it was originally. Water does not have to be completely pure to be considered unpolluted.
- Natural waters are not completely pure. Rainwater contains dissolved salts in relative proportions similar to those in seawater, but over a thousand times less concentrated. Rainwater contains a greater relative proportion of dissolved gases, particularly carbon dioxide, than seawater, and this makes it slightly acidic. River water has a composition different from both rainwater and seawater; it has a greater concentration of dissolved solids (TDS) than rainwater, and may contain suspended solids. Groundwater usually has slightly greater TDS values than surface water, and varies in composition, depending on the rocks through which it has passed. The TDS value of groundwater depends on the length of time the water has been in contact with rock, so slow-moving, deeper groundwater has a higher TDS value.
- Pollution can come from many different sources, including domestic sewage, farms, industry, mining, quarrying and cooling. There are many types of pollutants, including natural organic materials, living organisms, plant nutrients, organic and inorganic chemicals, sediments and heat.
- Water often has to be treated before it is of suitable quality for use. The quality needed depends on the use to which the water is to be put; quality standards for public water supplies are set by the WHO, the EU and some individual countries; but the quality required for industrial water and irrigation water can vary.
- Sewage treatment aims to reduce the amount of organic and suspended solid material present, remove toxic materials and eliminate pathogenic bacteria, mainly by settlement or biological processes. The effluent is discharged into rivers, lakes or the sea, and the remaining sludge may be dumped at sea (but not in the EU), disposed of on farmland, dumped in landfills or incinerated.