## 2 Materials and Methods
### Calculating Procedures
#### 2.5.3 Effect of Water Quality Constituents on Irrigation Infrastructure  
Irrigation water is normally supplied untreated. It is, thus, not chemically stabilised to control the potential for the corrosion or encrustation of irrigation equipment or filtered so that it can be used directly for drip irrigation. The corrosion and scaling of irrigation equipment and infrastructure are arguably the primary water quality problems associated with on-farm irrigation infrastructure. Either can necessitate the early replacement of expensive irrigation equipment. Both corrosion and scaling are the result of water having chemical imbalances. A secondary problem associated with water constituents is the clogging of drippers, which can be of chemical, biological, or physical origin. 1. Corrosion or scaling of irrigation equipment  
Although minor scaling, which forms a protective layer against corrosion inside pipes, is normally considered beneficial, excessive scaling reduces flow rates and damages water systems, necessitating repair or replacement. The most common cause of scaling is the precipitation of calcium carbonate when saturation is exceeded. Calcium carbonate precipitation increases with increasing temperature, with the result that calcium carbonate frequently precipitates in slow-flowing dripper lines. Although less frequent, gypsum precipitation also occurs in irrigation equipment when water high in calcium and sulphate is used. Gypsum precipitation is a common problem when gypsumgysiferous-neutralised acid mine drainage is used for irrigation. There are several indices with which corrosion and scaling can be predicted. The most commonly used index is the Langelier Saturation Index (LI), which was developed by [PERSON] in 1936. The LI is an approximate measure of the degree of saturation of calcium carbonate in water. It is widely used as an index of the likelihood of corrosion and scaling and is calculated as the difference between the actual measured pH of water (pH\({}_{\text{a}}\)) and the hypothetical saturation pH of the water (pH\({}_{\text{s}}\)), i.e., the pH at which water with a given bicarbonate and calcium ion concentration and temperature would be in equilibrium with solid CaCO\({}_{3}\)[8]. A positive LI indicates that water is over-saturated and scaling is likely. However, a negative LI indicates water that is under-saturated with respect to calcium carbonate and potentially corrosive. LI values between \(-0.5\) and \(0.5\) should not lead to corrosion or encrustation problems. Serious corrosion is likely if LI is in the range of \(-0.5\) to \(-2\), and similarly, scaling will be problematic between values of \(0.5\) and \(2\). 2. Clogging of drippers  
The low flow rates of drip emitters are conducive to clogging problems. While it is relatively easy to spot blocked emitters of surface drip systems, it is very difficult to distinguish one that is partially blocked from one that is not. Both blocked and partially blocked emitters alter the hydraulics of the entire system, result in a decrease in the uniformity of application, and give rise to reduced crop yields. The topic of clogging in drip irrigation systems, the role of water constituents in emitter clogging, and available treatment options are reviewed elsewhere [2; 23]. Suspended solids, such as sand, silt, and clay, as well as organic matter, can easily block emitters. The problem with suspended solids can usually be addressed through prior sedimentation and filtration. No problems are expected if suspended solids are below 50 mg/L, while severe impacts can arise if this increases to 100 mg/L or more. The chemical precipitation of substances such as lime, iron, manganese, and phosphates can also cause clogging. The Langelier Index is often used to predict clogging by lime precipitation. As a general rule of thumb, problems can be expected when pH exceeds 8. Iron in the soluble ferrous form can be oxidised into the insoluble ferric Fe\({}^{3+}\) form and cause clogging.