Background Notes

Introduction

The data used to compile this release were received by the CSO from Irish Water in response to a request made under the Statistics Act, 1993.

Revisions

All figures are subject to revision. Water meters can store data for previous readings and they are typically read using drive-by technology. Not all meters may have been read for the full release period e.g. if the last data collection for an area was done during December then data for December will not be available until the meter is read again and the data are made available to the CSO. Therefore a full year's data may not be available for some meters.

Timeliness

This release is based on meter readings. To calculate consumption for any meters that were not read on the 31st December of the year being published, the CSO uses meter readings from the subsequent year as soon as they become available. It is hoped to publish 2018 data in the coming months.

Thresholds

Table 2 in the release examines the impact of using consumption thresholds to exclude data that are unusually high. These thresholds show the substantial impact that high usage has on the average consumption figures. Typically, high consumption is due to a leak.

Median

The difference between the average and the median gives an indication of the extent of high consumption as the median is less influenced by the small number of meters with very high consumption. In Table 2 the median is calculated from annual 2017 data for a meter whereas in Tables 1, 4B, 5B and 6 it is calculated from monthly data.

Coverage

The data used in this release only cover metered usage. Apartments, many group water schemes, and abstractions from wells are not included. The 2017 data are based on 707,854 meters. Data from meters are included provided a full month’s data could be calculated from the meter readings. Some meters may not have been read during 2017.

Methodology

Irish Water provided monthly files of meter readings to the CSO. The files contained both meter readings and derived consumption data. The dates of the meter readings are generally from a date that is at the end of the month but readings can also occur on other days of the month and in some cases a meter may not have been read in a particular month.

In a small number of cases, a meter was read more than twice in a month. In these cases the CSO has used the first and last readings in a month to calculate monthly consumption.

Meter readings that were irregular in the series, e.g. readings lower than previous readings, have been excluded. Before excluding any readings, the CSO has examined in detail the series of readings for meters where there was a decrease of 500 cubic metres or more between two readings. The higher reading was excluded if it was the irregular reading in the series.

The CSO has converted the readings into monthly usage figures by allocating the difference in two readings proportionately between the dates that the meters were read. Months with partial data have been excluded e.g. if the last reading for a meter was before 31st December, and there were no meter readings available yet from the following year, then that month was excluded.

Measurement units

The meter readings are in cubic metres. One cubic metre equals one thousand litres. The readings in cubic metres have been converted to average and median consumption in litres per meter per day. In Table 1, the data were converted into average and median consumption per meter per day in each month.

County data

There was a relatively small number of meters installed in Dublin 17 and Dublin 24. No meter data were available for Dublin 10.

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