We have a duty to ensure that water is used wisely by our customers. However, this information is aimed at developers, architects, designers and installers, who are encouraged to pass on the following advice to their clients and our customers. It presents an overall view of our requirements and summarises measures that may be undertaken to enable our customers to conserve water and at the same time conserve energy in relation to treatment processes, water supply and efficient waste water disposal.

The demand for water will increase in the future. Climatic changes are likely to affect rainfall, runoff and demand during the summer months as it become warmer and drier - hence the growing need to conserve water. Drinking water requires energy both for its treatment and to pump it to its destination. Reducing water consumption therefore also reduces energy consumption.

Indirect benefits arising from water conservation lead to energy savings related to supply, treatment and process costs and reduced disposal costs, trade effluents etc. Industrial customers with metered supplies already have every incentive to economise on water use.

There are numbers of ways that conservation of water may be achieved. These include:

The Water Supply Byelaws 2002 (the Byelaws) allow the installation of dual-flush WC flushing cisterns. Installed and used correctly they can achieve considerable water savings. The Byelaws require a reduced maximum volume of water flushed in newly installed WC cisterns – from 7.5 litres down to 6 litres. There is no prescribed lower limit. Only those flushing devices which meet the stringent specification approved by us will be allowed - these include drop valves. Mains pressure flushing valves and pressure flushing cisterns which are permitted in certain non-domestic premises. We encourage the use of displacement devices in existing flushing cisterns provided they do not lead, by repeated flushing, to a greater water use. There are proprietary devices available as alternatives to Save-A-Flush sachet but they must be used judiciously. Their installation must not result in additional flushing to remove faecal material nor must the displacement device impede the action of the float operated valve. We will permit the retrofitting of dual and interruptible flushing devices to WC cisterns which were installed before 1 July 1999. These Byelaws cisterns use 7.5 litres or more per flush and savings of 25% in water use have been shown in trials where dual flush was introduced. Retro-fit devices must not alter the available full flush volume and must meet the relevant parts of the current WC performance specification. There must be clearly a discernable method of operating the different flush volumes and clear operating instructions must be displayed on the cistern or nearby. The efficient operation of flushing mechanisms should be routinely checked.

The Byelaws require automatic controls on urinal flushing cisterns. Automatic and proximity controls allow great water savings. These also provide period flushing when there has been little or no use, i.e. no flushing in silent hours and at weekends. Water-less urinals are now available. However it is necessary to evaluate the cost of cleaning chemicals and manpower against the savings from fewer water fittings and the use of water. 

Infra-red or ultrasound sensors (proximity switches) can be provided to control the flushing of urinals and supplies to basin taps. Such sensors, in providing supplies precisely when required, save water. 

Properly adjusted for length of time and flow and well maintained, self-closing taps at basins and as controls for showers in schools and municipal buildings effect significant water savings. Taps, with spray outlets, either self-closing or of the manually closing type, can also reduce water consumption and may also be used with basins without plugs in certain circumstances – where spray taps discharge less than 3.6 litres per minute. Otherwise, basins shall always have plugs. The spray outlets of taps and the roses of shower outlets accumulate a manganese based scale in certain parts of the Island. Outlets should be cleaned regularly in order to provide a full, directional flow thereby discouraging repeated tap-opening actions leading to excessive water use. In areas of high mains pressures, flow restrictors in connections to taps will save water. 

Dripping taps should always be adjusted or the washer (or the ceramic disc) replaced. Water loss which may arise from a conventional tap is illustrated below.

Amounts of water loss from a tap

Careful attention to pipe-work design can reduce the amount of cold water that runs to waste before 'the hot water arrives'. Care should be taken to route or lag pipes carrying water intended for drinking in order that it will not be warmed. Pipes carrying hot water should also be lagged to prevent heat loss and thereby reducing draw-off of tepid water. The smaller the bore of the hot water pipes, the less water is drawn off when hot water is required at the tap. 

Washing and dishwashing machines and other water using appliances that use the minimum amount of water or have the ecolabel should be specified. The manufacturer's instructions supplied with an appliance will indicate the volume of water use.

Warning pipes should be checked for discharge and remedial action taken to adjust or replace the washers of associated float operated valves. The floats of all float operated valves should be checked from time to time to ensure that they do not contain water, thereby sitting lower in the water and allowing the water level to rise above the correct water line. Lagging cisterns prevents undesirable tepid draw-off water temperatures in summer and freezing of water in winter.

'Point of use' heaters eliminate cold water run off. Heat sources and hot water storage vessels should be situated as close as possible to hot water outlet taps, to reduce cold water run off. 

Power showers (pump-driven) use more water than showers that are not pump-driven. Instantaneous showers (having a point of use heater) may use less cold water at initial draw off, than a shower connected to a hot water system. Low-flow shower heads can provide an effective shower.

Careful attention to predicting requirements can reduce the volume of water which is to be stored in cisterns. This can reduce the amount of water that is stored but remains unused.

Please contact us if you intend to use any irrigation system supplied with mains water that is intended to operate while unattended. 

Swimming pools supplied with water from the mains should be covered when not in use in order to reduce evaporation. The Byelaws require that we are notified of the construction of pools containing over 10,000 litres. Pools should be checked from time to time to ensure that they remain watertight. 

In areas of high mains water pressure, pressure reducing valves can reduce water wastage.

Car and vehicle wash plants should be installed that incorporate water recirculation facilities.

Greywater recycling systems for WC flushing and garden watering may only be connected to the mains water system via an air gap providing fluid category 5 backflow prevention (for example, Type AA or AB air gap).

Always use products and materials listed in the Water Regulations Advisory Scheme's Water Products and Materials Directory


Lawn sprinklers are to be discouraged and must never be left on overnight. Watering gardens and hanging baskets by a hand held watering can will use less water than the use of a hose. Garden hoses should be fitted with self closing flow controls at the outlet end.

Water butts

Water butts at rainwater downpipe outlets should be used for retaining rainwater for garden watering. There are systems available which will allow the use of rainwater for toilet flushing. However, there must be no physical connection between the public drinking water supply system and the rainwater system or any system where used water i.e. bath water, is used for flushing toilets or garden watering. 

It is important to know the difference between leaks and bursts;

Bursts are complete pipe failures where immediate repair is necessary to prevent customers being without water

Leaks are failures where water is leaking but the pipe continues to supply water. These are often called discretional leaks where a water supplier might decide to postpone repair (or not repair at all as the small loss of water is not worth the cost of the repair).

First the technical bit

Leakage (or unaccounted for water to be correct) is a sum of the difference between the expected lowest flow period each day and the actual low flow at the same period each day for all the distribution management zones that we have. We do it the same way as the water companies in the UK. Like all water companies and suppliers we have a leakage rate that we would like to improve upon and we constantly work to do this.

Leakage is not just in our pipes. The leakage from our customers pipes and plumbing is also included in the calculation.

There are challenges which add difficulty into having a low leakage rate;

  1. If your Infrastructure is old then it is more prone to leaking and bursting.
  2. If your topography (you have a hilly landscape) is challenging it means you have to have high pressures to get over hills. High pressure = higher leakage.
  3. If you have long lengths of pipes running through countryside with very few customers then the proportion of pipe vs customers is greater and the calculation works against you.
  4. If you do not meter your customers water supplies (don’t charge by unit used) and if your customers have a culture of not conserving water.

Sadly we tick all these boxes and so we have all the challenges. We are similar to Scottish Water in this regard. The biggest practical challenge is that our 1700km of water mains are buried (mostly under our roads and streets). Small leaks are hard to find. We use latest technologies to find leaks but the biggest source of leakage is almost certainly the millions of tiny leaks that, short of digging up the whole Island, are virtually impossible to find and repair.

In terms of comparison we appear, on first inspection, to compare poorly on litres/property/day because of the points above but we do compare favourably in terms of leakage/km of water main and both of these are to be expected.

We use a standard method of measuring leakage which is compliant with the OFWAT requirement in the UK. We are regularly audited on our method and assumptions. Our Island is divided into 72 Distribution management areas (DMAs). These are discreet zones where there is only one flow route in and that is metered. The flow meters on the inlet are logged and each day we download the 24 hour flow profiles using a proprietary piece of software called PMAC. We know the number of properties in each zone and we have a standard flow rate that is the expected lowest flow from a property at a given time of day. The leakage is the total flow at the lowest point - no. of properties x the expected flow.

A key point to note is that this includes all our network plus all our customers own supply pipes and plumbing systems. So leakage is not just our problem but it is also a problem for our 40,000 customers. For example, if a customer chooses to run his/her sprinkler all night (as he/she is entitled to do) this would count as ‘our’ leakage.

Leakage is measured in three key ways:

  1. ML/day lost
  2. Litres/Property/Day
  3. Cubic Metres/km of water main

The popular method in the UK, and the method by which companies in England and Wales are legally obligated to report is ML/day. Their targets are all set around this figure. This unit of reporting gives no easy comparison and is not a measure that we focus on. We focus on litres/property/day for the purpose of our Key Performance Indicators.

This table compares the performance of some water companies in the UK

Water Supplier

Ml/day lost


m3/km mains/day

Manx Utilities




Thames Water




Yorkshire Water




United Utilities




Anglian Water




Northumbrian Water




Scottish Water

500 (approx)



Data for English water companies from www.discoverwater.co.uk  

You will see that we appear to perform poorly when we consider litres/property/day. This is influenced by the challenges we have including our low population density. However, when we consider m3/km (the amount of water lost per kilometre of main) we perform exceptionally well.

Leakage is one of our Key Performance Indicators. It ranks alongside water quality and customer minutes lost. We have the following initiatives to reduce leakage:

  • We always repair leaks on our system as soon as we find them. We do not apply a discretionary approach or consider economic cost. We repair all leaks (on our network) as soon as we find them.
  • We actively encourage customers to repair leaks on their supply pipes when we detect them. We do this by giving them advice and we help to find leaks on their properties. In some cases we use enforcement action and the powers that we have if a customer is wasting water through leakage and refuses to repair their supply pipes.
  • Whenever the DOI are undertaking road relaying/reconstruction we take the opportunity to replace the water mains at the same time.
  • We are currently renewing our fleet of DMA flow loggers and upgrading to a new leakage software system called Watercore. This will give us much better information (in the office and remotely) about the flows in our system and this will help us to reduce shock waves within the water network. The improved data and smart alarms will reduce leakage detection times and enable network calming and pressure management.
  • We are looking at further optimising the setting of our Pressure Reducing Valves (PRVs) in the system and for some of them making them more ‘smart’ in the way they operate (e.g. reducing pressures at night when flows are low and pressures are high). We use our Hydraulic Model to assist in assessing improvements.
  • We have a scheme to install 19 new PRVs in the system with an aim to reduce leakage and bursts whilst still meeting customer desire for water pressures.

We have over 1700km of water mains and communication pipes. On top of this, you, our customers have many kilometres of supply pipes. To renew all these water mains and pipes would be an enormous project and because many water mains are under our footpaths, streets and highways, it would cause untold congestion. The cost of renewing water mains is in the order of £200 per metre. If you multiply this by the length of mains we have you will see the magnitude of the problem.

We invest around £1M per year in renewing water mains.

The Water Supply Byelaws 2002

The Byelaws Inspector can be contacted by telephoning (01624) 687687.

The Water Regulations Guide outlines the regulations along with the Water Industry's recommendations for complying with them. It is published by and available from WRAS.

The Water Products and Materials Directory lists products which have been tested and approved by the water suppliers for their compliance with the regulations.

Environmental Technology Best Practice Programme

Guide GG26: 'Saving money through waste minimisation: Reducing water use'

Guide GG67: 'Cost effective water saving devices and practices'

Environmental Agency: 'Conserving Water in Buildings' – a series of fact cards, other leaflets and advice. 

Waterwise UK

We are now a proud supporter of Waterwise; a not-for-profit organisation helping communities, businesses and governments to understand the value of water and use it wisely so that we have enough now and in the future.  You can find out more ways to save water by visiting the Waterwise website.