Water Quality
1. Water quality parameters
Water generally contains various components, which either come from the natural environment itself or have been introduced as a result of human activities. To characterise water, various parameters are determined which represent its physical, chemical and biological characteristics. These parameters are indicators of water quality and constitute impurities when they reach values higher than those established for a given use. The main indicators of water quality are discussed below, separated into physical, chemical and biological aspects.
Physical Parameters
a) Temperature: a measure of the intensity of heat; it is an important parameter because it influences some of the water's properties (density, viscosity, dissolved oxygen), which affects aquatic life. Temperature can vary depending on natural sources (solar energy) and anthropogenic sources (industrial waste and machine cooling water).
b) Taste and odour: result from natural causes (algae; decaying vegetation; bacteria; fungi; organic compounds such as hydrogen sulphide gas, sulphates) and artificial causes (domestic and industrial sewage). The drinking water standard: completely odourless water.
c) Colour: results from the existence of substances in solution in the water; can be caused by iron or manganese, the decomposition of organic matter in the water (mainly vegetables), algae or the introduction of industrial and domestic sewage. Drinking water standard: colour intensity of less than 5 units.
d) Turbidity: presence of suspended matter in the water, such as clay, silt, finely divided organic substances, microscopic organisms and other particles. The drinking water standard: turbidity of less than 1 unit.
e) Solids: Suspended solids: residue that remains on an asbestos filter after filtering the sample. They can be divided into:
- Sedimentable solids: sediment after the sample has rested for a period of t
- Non-settling solids: can only be removed by coagulation, flocculation and decantation processes.
Dissolved solids: material that passes through the filter. They represent the matter in solution or in a colloidal state present in the effluent sample.
f) Electrical Conductivity: the ability of water to conduct an electric current. This parameter is related to the presence of dissolved ions in the water, which are electrically charged particles. The greater the quantity of dissolved ions, the greater the electrical conductivity of the water.
g) Phosphorus: is found in water in the forms of orthophosphate, polyphosphate and organic phosphorus; it is essential for algae growth, but in excess it causes eutrophication; its main sources are: dissolution of soil compounds; decomposition of organic matter, domestic and industrial sewage; fertilisers; detergents; animal excrement.
h) Fluorides: fluorides have a beneficial effect in preventing tooth decay; in higher concentrations, they can cause changes in bone structure or dental fluorosis (dark spots on the teeth).
i) Dissolved Oxygen (DO): is essential for aerobic organisms; water under normal conditions contains dissolved oxygen, the saturation level of which depends on altitude and temperature; waters with low dissolved oxygen levels indicate that they have received organic matter; the decomposition of organic matter by aerobic bacteria is generally accompanied by the consumption and reduction of dissolved oxygen in the water; depending on the self-depuration capacity of the source, the dissolved oxygen content can reach very low values, or zero, extinguishing aerobic aquatic organisms.
j) Organic matter: organic matter in water is necessary for heterotrophic beings to nourish themselves and for autotrophs as a source of nutrient salts and carbon dioxide; in large quantities, however, it can cause problems such as colour, odour, turbidity and consumption of dissolved oxygen by decomposing organisms.
Oxygen consumption is one of the most serious problems with increasing organic matter content, as it causes ecological imbalances and can lead to the extinction of aerobic organisms. Two indicators of organic matter content in water are generally used: Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD).
l) Biochemical Oxygen Demand (BOD) is the amount of oxygen needed to oxidise organic matter by aerobic bacteria. It therefore represents the amount of oxygen that would need to be supplied to aerobic bacteria in order for them to consume the organic matter present in a liquid (water or sewage). BOD is determined in the laboratory by observing the oxygen consumed in samples of the liquid over 5 days at a temperature of 20°C.
m) Chemical Oxygen Demand (COD): the amount of oxygen needed to oxidise organic matter using a chemical agent. COD is also determined in the laboratory, but in a much shorter timeframe than the BOD test. For the same liquid, COD is always higher than BOD.
n) Inorganic components: some inorganic components of water, including heavy metals, are toxic to humans: arsenic, cadmium, chromium, lead, mercury, silver, copper and zinc; in addition to metals, cyanides can be mentioned; these components are generally incorporated into the water through industrial discharges or from agricultural, mining and quarrying activities.
o) Organic components: some organic components in water are resistant to biological degradation and accumulate in the food chain; these include pesticides, some types of detergents and other chemical products, which are toxic.
Biological Parameters
a) Coliforms: these are indicators of the presence of pathogenic microorganisms in water; faecal coliforms are found in large quantities in human faeces and, when found in water, mean that it has received domestic sewage and may contain microorganisms that cause disease.
b) Algae: Algae play an important role in the aquatic environment and are responsible for producing a large proportion of the dissolved oxygen in the environment; in large quantities, as a result of excess nutrients (eutrophication), they cause certain inconveniences: taste and odour; toxicity, turbidity and colour; the formation of masses of organic matter which, when decomposed, cause a reduction in dissolved oxygen; corrosion; interference in water treatment processes: an unpleasant aesthetic appearance.
2. Water quality standards
The maximum levels of impurities allowed in water are established according to its uses. These levels make up the quality standards, which are set by public organisations with the aim of ensuring that the water to be used for a particular purpose does not contain impurities that could harm it.
Water quality standards vary for each type of use. Thus, drinking water standards (water intended for human consumption) are different from bathing water standards (water intended for primary contact recreation), which in turn are not the same as those established for irrigation water or water intended for industrial use.
Even among industries, there are varying quality requirements, depending on the type of processing and the products they produce.
One way of defining the quality of water from springs is to classify them according to their proposed uses, establishing criteria or conditions to be met.
"Water is life and quality is our business"