Water Quality

Physical Water Quality Factors

Physical water quality factors (PWQF) are influenced by all the foreign materials that do not dissolve in the water, and that can usually be seen with the naked eye. These materials pose problems primarily to the irrigation system.

Micro-sprayers and drippers have very narrow openings (0.25mm to 2.50mm diameter) and are blocked by any material that is too large to pass through, or that accumulates in this narrow pathway. When partly or totally blocked, the micro-sprayer or dripper cannot deliver the required volume of water to the trees.

The following materials influence the physical quality factors and are often responsible for clogging the drippers or micro-sprayers:

• Inorganic materials, such as clay, silt and sand.
• Organic debris, such as remnants of plants, seeds, animals, aquatic fauna and flora.
• Living aquatic plants and animals, such as algae and snails.
• Plastic cuttings from the irrigation pipes and equipment.
• Lubricant residues.

While the first three contaminants can usually not be controlled and must be managed, the last two contaminants can be controlled by taking the necessary steps to prevent contamination by plastic cuttings and lubricant residues.

Sprinklers do not block as easy as micro sprayers but also do block causing uneven distribution of water.

Chemical Water Quality Factors

The chemical water quality factors (CWQF) refer to the non-visible components in water. Instruments are used to determine their presence and concentration. CWQF are very important, because they determine the short- and long-term potential and sustainability of the entire plant production system. Chemical quality factors affect:

• Crop production.
• Sustainability of the productivity of the soil.
• The effective operation of the irrigation system.

The most important CWQF and their impact on each of these areas are shown in the table below, with the following classifications:

• Y = This factor has an impact.
• Y/N = This factor may have an impact depending on other factors.
• N = This factor seldom has an impact.

pH: pH indicates the acidity or alkalinity of any substance, in this case, water, on a scale of 1 to 14. pH can range from 1 (extremely acidic) to 14 (extremely alkaline). A pH value of 7 is neutral. Plant sap has a pH of 5.8 and the pH of human blood is almost 7. Water with a low pH is referred to as acidic. Water with a high pH is referred to as alkaline.

Water Quality Management (WQM)

Remember

• Irrigation is used in crop production to supply plants with the water they need in addition to rainfall.
• Water quality factors are important depending on the type of irrigation system used. Micro-sprayer irrigation is the most commonly used in South Africa and drip irrigation is the second most common.
• Water dissolves many substances, such as salts, and is a carrier for a lot of suspended material, which influences the water quality, and which is why it is polluted too easily.
• Water quality management (WQM) has to do with managing foreign material in the water, and not with the water itself.
• Water quality management concerns six critical control points, being:
• Determining the quality of the water received on the farm.
• Identifying the causes of the said quality.
• Being aware of the quality standards of water for crop production.
• Improving the quality of received water where possible.
• Identifying water quality factors that cannot be improved and need to be managed; and
• Managing the quality of the water leaving the farm.
• PWQF is determined by the foreign material that does not dissolve in the water. These materials can clog emitters and pipes.
• CWQF refer to the non-visible qualities of water and affects crop production, the sustainability of the soil productivity and the effectiveness of the irrigation system.