Centralized water distribution in developing countries continues to be fraught with great difficulties. One major deficiency is the intermittent distribution of water. Most distribution systems were originally designed for a continuous supply mode and are now operated intermittently because of various constraints. In this mode of operation, the piping system is supplied with water for limited periods of time and is not filled with water under pressure continuously as originally provided for in the technical design concept. Periodic filling and draining of the pipe system is associated with numerous negative consequences which ultimately aggravate or prevent sustainable safe water distribution. To overcome this problem, thorough knowledge of intermittent water distribution is required. This paper discusses possible causes and consequences, and their interactions. These considerations are largely limited to the technical side of water distribution and are mainly based on the technical literature in the field.
In many areas of the world water distribution systems are operated intermittently. The alternate filling and emptying of the pipe network leads to effects, which have negative impacts on water meter accuracy. For example, air that is present in the pipe network due to the emptying process must exit the network during the subsequent filling process. A part of this air is discharged through service connections and, thus, through water meters. In this paper, a study is presented in which the measurement error of single-jet and multi-jet water meters due to the filling process of an empty pipe is investigated experimentally. From the start of air flow to the steady-state flow of water, several causes of measurement errors can be distinguished, such as pure air flow, the impact of the water front on the impeller, the existence of two-phase flow or unsteady flow conditions. For both meter types, it has been discovered that the measurement error is mainly caused by the air flow. The experimental results show that up to 93% of the air volume in the pipe is registered by the water meters. Based on these results, an approach for estimating the measurement error for both meter types is presented.
Establishing a water balance is a precondition of efficient water loss management in water supply systems. In this article, the applicability of available standards and methods for establishing the water balance is reviewed on the basis of an evaluation of literature in the field. In principle, establishing the water balance is made straightforward by measuring, estimating, and calculating the components of the water balance. However, water balances are often established that do not cover all components or are based on rough estimates. In most cases, water balances are determined for a whole network, not for zones, and only at long, mostly yearly, intervals, resulting in limited informational value of the findings. The main reasons for this seem to be the effort involved, the limited availability of data, and the lack of adequate methods for determining unmeasured components. This article concludes that there is a need for developing methods and tools to support water utilities in establishing complete, zonal water balances with reasonable effort.
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