The Public Authority for Electricity and Water in Oman carried out an initial estimate of legitimate domestic night consumption (LDNC) based on an assessment of night consumption surveys of over 1,500 premises. However, no allowance for meter under-registration (MUR) had been applied in the assessment. This paper reports on a study to identify MUR in Oman, which can be applied to the results of the survey for LDNC. All premises in Oman are required to have a roof tank in order for customers to maintain their supply in the case of mains water supply interruptions. Regulations require that the roof tanks provide at least two days' storage. It is believed that roof tanks could have a significant impact on MUR due to the long ‘tails’ generated by the operation of the ball valve controlling the refilling of the roof tank. It was therefore decided that a study should be carried out to review the main drivers for MUR and the likely level of MUR to be expected in Oman, particularly at low flows such as those experienced at night time when a single toilet is flushed. In regards to the sample of properties included in the MUR survey, it was suspected that in the case of apartment blocks, the revenue meters will normally be located after the roof tank, in which case the roof tank will not influence MUR. This study sought to confirm this. Half the premises were fitted with an unmeasured flow reducer on a bypass so that the potential of such devices to reduce MUR could be investigated. Oman has continuous water supply. There were no supply interruptions during the study. The paper describes details of the plumbing arrangements developed for the study and the results established as part of the programme. It also takes the opportunity to report on the level of daily and night consumption experienced on the study area.

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