1. BACKGROUND

The existing water supply in the Greater Dublin Region is undertaken by seven local authorities within their respective functional areas. Two local authorities have responsibility for water production in the Region.

Historically, water demand in the Region has been rising steadily. As each new increment of production capacity has been added, it has been absorbed almost immediately to meet suppressed demand. Given that there is a finite limit to the economic and practical water resources available in the Region, it was clear that this demand growth pattern of 2% increase per annum is unsustainable in the long term particularly since it was believed that leakage accounts for a large proportion of the demand. At the same time, there was an urgent need for residual capacity in the Region to meet demand growth, both domestic and industrial/commercial in the light of significant economic growth in the period 1994-1996.

Against this background, the Department of the Environment commissioned a Strategic Study of the Water Supply of the Greater Dublin Region in January 1995. The Study was carried out by Compagnie Générale des Eaux (General Water Company) in association with M.C. O'Sullivan & Co.Ltd. with the Final Report submitted in January 1996. The main purpose of the study was :

a) to assess present levels of service and water supply problems in the Region

b) to provide for the cost effective future development of the water supply network for the Region.

2. PRELIMINARY DATA COLLECTION

In order to develop a comprehensive understanding of the existing system, its capacity and shortcomings, an extensive data collection exercise was undertaken. In approaching this exercise, the Study Team objectives included :

• Determination of existing levels of service
• Comprehensive understanding of existing demand and water balance in the Region
• Assessment of available water resources and treatment capacity
• Assessment of hydraulic conditions and limitations
• Development of an asset register and asset condition statement having regard to integrity, water quality impacts and general condition
• Management and operational issues
  
  

The principal areas of data collection and analysis were :

• Mains Records; all available mapping of the trunk and distribution mains networks was obtained and used to create a mains inventory characterised by local authority, map reference, street reference, size and material. The basic source comprised paper based record drawings which were reasonably comprehensive for most areas.

• Mains Condition Data; information on mains condition was sought by reference to burst data, public complaint registers, examination of pipe samples and from available reports.

• Demand Breakdown; assessment of water demand was based on population statistics and numbers of properties using the 1991 census updated to 1995 from consideration of development trends. Metered industrial demand records were obtained for all metered industry and numbers of unmetered trade consumers were established in each local authority area from water supply billing and other institutional records.

• Treatment Plant Production and Trunk Main Flows; the volumes of water produced and distributed in previous years were studied, having regard to recorded treated water production and major trunk main flows.

• Water Quality Data; available water quality data from routine analysis was obtained and assessed for compliance with the Drinking Water Directive and for assessment of impact on water quality within the distribution system.

• Water Quality Surveys; an extensive survey programme was undertaken which included sampling at 82 locations throughout the distribution system, in-situ testing for colour and chlorine residual, completion of consumer questionnaires and the taking of 30 samples for determination of lead concentration. Hydrant flow surveys were also carried out with colour determination and the entire data set was evaluated to determine changes in colour, turbidity and iron concentration profiles within the distribution system.

• Mains Age Profile; development maps of the region were procured to provide indication of age profile of mains and service pipes and this was cross referenced in interviews with operational personnel.

• Soil Corrosivity; soil maps were obtained and considered along with evidence of external corrosion in iron pipe samples to assist in evaluating the corrosion characteristics of the different areas.

• Land Use Studies; land use trends were evaluated from development plans. Industrial plans, land banks and stated development policies.

• Operational Issues; extensive interviews were carried out with technical and administrative staff in the local authorities to provide additional information on technical issues, establish key issues and shortcomings, maintenance procedures, budget outlines and details of the organisations themselves.
  

3. ASSESSMENT OF CURRENT DEMAND

During the study period the average demand in the region was determined from the combined production capacities of the 4 treatment plants, all of which were operating at full capacity. The daily output was calculated at 437.5 Ml/day.

During this period, throttling as a means of demand suppression was practised throughout the region. It follows that there was a degree of suppressed demand which was taken as being 15 Ml/day giving a true demand of 452.5 Ml/day. The estimated population in 1995 was taken as 1.22 million persons.

Extensive investigations were carried out in an effort to assess the components of demand in the region. Reference was also made to figures from the UK and Europe for average per capita consumption and typical usage by commercial enterprises.

The estimated breakdown of present demand was established as follows :

• Domestic Demand; domestic consumption was calculated at 135 l/h/day giving a total domestic consumption of 165 Ml/day. A figure of 60 l/property/day was assumed for house losses, equivalent to a total domestic consumption of 153 l/h/day or 187 Ml in total.

• Trade Demand; billing records for metered and unmetered industrial and commercial consumers were examined in detail. The overall proportion of industrial and commercial consumers which are metered is relatively small, though it would be expected that they are the larger users who would account for the vast majority of trade consumption. The total metered consumption in 1994 was estimated at 74 Ml/day.

For a minimum pressure standard of 15m, it was estimated that some 127,000 properties or 34% of the total had unsatisfactory pressure.

There are approximately 6,000 commercial consumers in the region with fixed charge accounts. There are no accurate estimates of consumption for these and the estimate used was derived from the amount charged at commercial rates. In addition, there are approximately 25,000 rateable properties which are uncharged and can be described as unmeasured non-domestic users. It is believed that these premises are typically professional offices and shops.

Consumption was estimated arbitrarily on the basis of 6 persons/property and 60 litres/person, giving 360 litres/property/day. Reference to UK practice in this regard was not particularly helpful in this context, showing a wide variation and is generally regarded as a balancing figure taken along with other unknown components such as per capita consumption and leakage. The estimate of unmetered industrial and commercial consumption ultimately derived was 17.1 Ml/day.

4. FUTURE DEMAND FORECAST

A future demand forecast to the horizon of 2016 was developed having regard to the following component elements :

• Domestic Demand; for projected population figures and per capita consumption

Existing Industrial/Commercial Demand; projected change taking account of increased output, environmental pressures and application of the " polluter pays principle ".

• New Industrial Demand; reasonable provision for major new industrial development in zoned lands and having regard to development plans for industrial parks in the region.
• Losses; assuming an active leakage control programme, realistic targets would be set for distribution and customer side losses.

4.1 Future Domestic Demand

It was recognised that some growth would occur in domestic demand in the region based on the rate of growth in house numbers, the continued fall in house occupancy rate and increased prosperity. Population growth from historical census data and the rate of growth of residential development was anticipated to grow in urban areas. An overall figure of 0.6% per annum was adopted for the Region as a whole equivalent to approximately 14% from 1994 to 2016. It was recognised that the bulk of this would take place in peripheral areas.

Per capita consumption is also influenced by increased prosperity, additional appliances, increasing use of power, showers and recovery from suppressed demand. Even when offset by domestic conservation policies, a figure of 0.6% per annum compound growth in per capita consumption was assumed. This rate of growth was identified from a study of micro-components of consumption in England and Wales as part of the National Rivers Authority's National Water Resources Strategy. The effect is to increase per capita consumption from 135 l/h/day in 1994 to 154 l/h/day by 2016.

4.2 Future Industrial Demand

Water consumption in existing industry might be expected to grow in a high performance economy associated with increased production. However, opposite factors which will tend to reduce consumption will include water saving measures associated with improved housekeeping, increased charges for effluent treatment and greater efficiency. Accordingly, no change in current demand for existing industry is assumed.

National and local policies promote continued industrial development throughout the Region with extensive areas of lands zoned for industrial development totalling approximately 1,800 hectares currently. In all, it was considered prudent to provide for an increase of 48 Ml/day over the study period to cater for industrial development. This was distributed throughout the Region according to the areas available for development and the types of industry being encouraged in the particular areas.

4.3 Future Loss Objectives

The other critical factor in estimating future demands relates to the projected level of losses. Based on an active and aggressive leakage programme discussed late, the following assumptions have been made as regards future losses :

• Distribution losses; to be reduced by half to approximately 20% at year 2000 and further reduced to 16% by the year 2016,

• Customer Pipe Losses; to be reduced to 50 l/property/day by year 2000 and to 40 l/property/day by the year 2016.
  

5. WATER QUALITY

Water quality issues in the context of the Study were considered in terms of compliance with the EU Drinking Water Directive (80/778/EEC). In relation to distributed water quality, the following observations were made :

• Iron concentrations in the distribution system with a significant percentage exceeding the maximum admissible concentration and substantial numbers of samples from routine sampling indicate undesirable high levels. This is consistent with the corrosive nature of the water and the extent of corrosion within the mains.

• Filter paper colour tests on distributed water and hydrant discharges confirmed the impact of corrosion products in the mains on colour with significant disimprovement in distribution dead-ends.

• Residual chlorine levels are low in the distribution system, particularly when related to the chlorine residuals at the treatment plants.

The most significant water quality issue relates to occasional failures in bacteriological standards due to the two open service reservoirs and the presence of significant numbers of ball hydrants in the distribution system. These can permit contamination of the supply.

The corrosivity of the water supply in Dublin is evident from the extent of corrosion of the cast iron pipe network and is reflected in the values for Langelier Index and Ryznar Index for the individual supplies. Notwithstanding this, the expected elevation of metal concentrations in the supply, in particular iron, lead and to a lesser extent copper are not borne out by the analytical results. However, distribution pipe samples clearly exhibit evidence of the corrosive nature of the water. The deposition of coatings within the supply pipes may have the effect of limiting the transfer of metals to the water during quiescent supply conditions.

6. DEMAND MANAGEMENT AND LEAKAGE CONTROL

The estimation of current losses summarised above indicated average losses of 44% with the assumption that 5% relates to customer side losses and 39% to distribution losses. this is equivalent to an average leakage level of 27 l/property/hour. Statistics from England and Wales indicate supply pipe leakage in the range 38-80 l/property/day with an industry average of 50 l/property/day. This is considered to comprise background leakage from joints and fittings of the order of 20 l/property/day with the balance associated with undetected bursts.

The factors contributing to excessive leakage in the Dublin Region include the following :

• Age and condition of the network; notably the corrosion of metal pipes and services.

• Materials used; apart from cast iron, leakage in PVC networks in the Region have resulted from poor pipe laying practices, susceptibility to third party damage and corrosion of mild steel bolts on ferrule straps.

• Traffic loading; traffic loading is a factor in causing defects due to abrasions from heavy goods vehicles and occasionally where the mains have inadequate cover.

• Operating pressures; excessive pressures feed leakage where high static pressures are achieved. The mechanism of throttling trunk mains as a means of controlling pressure is less satisfactory than the management of pressure zones in the distribution network.

• Leakage Control Policies; a policy of passive leakage control inevitably results in considerably longer periods for identification, detection and repair of leaks compared with an active leakage control policy. Lack of local metering and the limited degree of connection to the telemetry system are further factors in this regard.

• Leakage Monitoring Infrastructure; limited district metering coverage, particularly in the older areas of the city make the identification and monitoring of leakage levels difficult and render leakage control programmes less efficient. Modern leak detection equipment and personnel trained in its use are scarce.

A 5-year programme to reduce leakage to 20% would include the following components :

• Implementation of a co-ordinated region-wide programme of works on a project basis to be additional to the current operational programmes of the local authorities.

• An intensive programme of leak detection and repair.

• Project management and information management systems would be established to plan the project, implement monitoring systems and supervise the works.

• External specialist expertise would be combined with local skilled operational staff to achieve the leakage objectives and a corresponding improvement in the levels of service where required.

• The potential for establishment of district meter areas, water supply areas and pressure zones would be determined and implemented.

• Data from the repair programme would be used to identify mains requiring replacement having regard to unacceptably high burst history.

• Leakage achievement should be sustainable in the subsequent period involving technology transfer to the local authorities, achievement of infrastructural improvements and systems to enable the reduction of losses to be sustained and improved further.

The objectives recommended would involve reduction in total losses to 101 Ml/day at the year 2000 and further reduction to 90 Ml/day, notwithstanding the increases in demand in the meantime, by the year 2016. This would require a continued active leakage policy based on flow measurement, active leak detection, pressure management and infrastructural renewal.

Ultimately, the whole of the distribution network must be subject to regular leakage monitoring by appropriate district metering, with water supply areas monitored via the telemetry system. It is likely that continued infrastructure renewal will be required to include replacement of weak communication pipes or rehabilitation of mains with a burst rate of in excess of 5 per kilometre within a 5-year period.

Reduction in customer losses is also required to meet the medium and long term demand objectives. A systematic approach to detection of customer losses and enforcement of waste notices requiring repair is required. A uniform procedure is recommended to be adopted across the Region for active enforcement of these notices. At the same time, a programme to increase public awareness of water conservation issues will be required.

7. TELEMETRY SYSTEM

The existing telemetry system covers key strategic reservoirs and flow meters. In the short term, additional metering and pressure monitoring will be established throughout the network to cover discrete water supply areas and ultimately extending to the full district meter areas. The extension of the telemetry system would be developed to cover these elements and to integrate the systems used at the treatment plants.

8. APPLICATION OF PRINCIPLES

The Strategy Study recommendations have been adopted by the Minister and similar principles will be applied to all sanitary authorities. A guidance manual on water distribution network management and leakage control has also been issued. A preliminary water audit to establish the level of UFW is now required before any capital investment in new infrastructure is approved. Central Government will pay up to 50% of the cost of preparing network management plans or strategic studies and will fund up to 100% of the cost of leakage reduction/control measures on a project basis of limited duration and to meet specific targets. Up to 50% of the cost of mains rehabilitation/replacement from approved water conservation proposals will also be funded.