## 1 Introduction  
Water is a limited resource in many countries where agriculture is the cornerstone for food security, economic development, and poverty reduction. In general, agriculture is the biggest user of water worldwide accounting for 70-90% of water utilization [1, 2]. Most of the agricultural water use is for irrigation because its contribution to food security is very significant [3, 4]. While only 20% of the global agricultural land is irrigated, about 39% of the food supply across the world is produced under irrigation. Irrigation also improves the efficiency of production inputs, such as fertilizers, improved seeds, and agrichemicals [5]. However, water losses in agriculture, in particular irrigation schemes, are generally high [6]. In South Africa, where agriculture accounts for 62% of the national demand [7], the water losses from agriculture are estimated at about 45% of the water supplied [8]. Irrigation schemes are reported to account for about 27% of the water losses, with about 12% of the losses occurring in conveyance networks [8]. However, the challenge of water scarcity in South Africa goes beyond the losses in agriculture and the inefficiency of irrigation systems. In a review of challenges and opportunities for water conservation in South African irrigated agriculture, ref. [9] cited the impact of climate change as the major driver of water scarcity. South African irrigation schemes are under pressure to improve their water-use efficiency [10]. Efficient use of irrigation water is crucial for regions where water resources are diminishing [11]. Efficient water-dispensing irrigation systems and good water management are important for high water-use efficiency (WUE) in irrigation schemes. All types of irrigation systems can potentially be managed to achieve high WUE, but pressurised piped systems offer better prospects than surface flood irrigation methods. The main advantage of the piped systems is their adaptability to almost all crop types, variable topographic conditions, and soil types. However, the pressurized systems are more costly to install and manage than the flood irrigation methods. Modern low-pressure-requiring systems, such as drip, microjet, and micro-sprayer, systems are more efficient than traditional systems, such as impact sprinklers and pivots, in terms of water application [12]. For instance, the drip system, which applies water slowly but steadily at frequent rates, can save large amounts of water because evaporative losses are very low as the water is applied close to plants. A properly designed, installed, and managed drip system can achieve high water application efficiency in the range of 90-95% [10; 11] compared against other systems, such sprinkler systems, whose efficiency is around 70% [13]. High water-application efficiency results in water savings [14] and improves water productivity [15]. Another important aspect of drip irrigation is its ability to combine water and chemical applications, which saves time and labour, and improves the uniformity of chemical applications. The drip system is also compatible with almost all crop types due to its flexibility on row spacing. However, the adoption rate of the drip irrigation system is generally low [16] due to several challenges that include a high capital cost to install the system and the proneness of the emitter to clogging by accumulated salts and suspended materials in the water, which expose farmers to frequent cleaning and replacement schedules. Farmers also perceive irrigation to be synonymous with the wetting of the soil surface, which a drip system does not do appreciably. The application efficiency of irrigation systems is evaluated during design and operation of the systems [17]. System performance changes over time due to deterioration of equipment. Hence, it is important to assess performance [18; 19] to understand current levels and factors of influence [6; 20], which is crucial when trying to solve problems of irrigation development and management [1].