8. Water conservation and water saving practices and management
8.3. Water conservation and water saving in urban areas
8.3.1. General aspects
The main supply problems faced in urban centres include the over-exploitation and depletion of the water supply sources, their contamination, high costs of operation and maintenance of supply systems, increased competition with other water uses (agriculture. industry, recreation), the observation of water quality standards, and the avoidance of water wastes.
Cities often face a high incidence of leaks, the use of water-wasteful technologies, very low levels of water reuse, less appropriate water pricing and billing systems, water revenues that often do not cover costs, and a lack of public awareness of water scarcity. Unfortunately, these problems are more acute in water scarcity regions and less developed countries than in temperate climates and developed countries.
Urban water supplies are used in households, industry, and commercial areas, as well as for urban services such as city washing, combating fire, maintenance of recreational lakes and swimming pools and irrigation of recreational areas. Water conservation and water savings are required in all these domains, both in the hands of the users and directly by the municipal
authorities.
Municipal water services may be public or private. Despite differences in institutional arrangements, funding sources, water pricing and billing systems, and in relationships between water management authorities and their customers, water conservation and water savings may be approached using a common perspective.
Water conservation and water savings in an urban water system includes water metering, leak detection and repair, water pricing and billing, service performance, use of water in municipal and public areas and services, and development of public awareness on water saving. These items are developed below and the respective main issues, benefits and limitations are summarised in Table 8.4.
8.3.2. Monitoring and metering the water supply and distribution system
Metering is required at both the supply and distribution systems and at household connections. At the supply level, it concerns monitoring and measuring the water stored, being conveyed, and circulating in the distribution system. The resulting data produces information on the state of the system, and the respective variables. This information is vital for planning system developments and modernisation, for operation, maintenance and management of the systems in real time, and, in particular for planning and implementation of water conservation and water saving programmes. Metering at the household outlets is required for knowing the users consumption, for billing the customers in accordance with the respective water use, and for the support of measures to be enforced when water availability does not allow the supply to match the current demand.
Metering and monitoring the supply system has many advantages (Arreguín, 1994), mainly:
Provides for an updated knowledge on the actual volumes stored and the discharges flowing in the water conveyance systems and in the distribution sectors, as well as water pressure and water levels at key nodes of the networks.
Information on the supply and distribution network’s state variables allows establishing the real time balance between water availability and demand.
Generates information to assess the water supply balance in problem areas, namely where large differences in pressure may occur, and to evaluate the pressure distribution and uniformity along the distribution network, thus providing for improved management of the system.
Produces data to evaluate the actual hydraulic conditions of the system’s operation, including the detection of anomalies and malfunctioning of the networks, pumping stations, and regulation and control equipment.
Produces information for planning and implementation of both preventive and corrective maintenance programs for supply lines, distribution networks, electromechanical equipment, water treatment plants, and storage facilities.
Allows accurate planning of system extensions, developments, and modernisation.
Allows estimating the volumes of water not being billed, to better identify the factors causing system losses, and to provide a basis for revision or upgrading of the rating policies.
TABLE 8.4. Water conservation and water saving in urban areas
Issue Benefits Limitations Effectiveness
System monitoring and metering
Information on the system state variables
Estimation of system water losses, locations and causes
Base for planning water conservation measures
Support for implementation of water savings
High investment and operational costs, mainly when an information system is created
Needs an information system to be fully effective
High to very high
Metering Provides for fair billing
Allows for water conservation planning
Induces adoption of water savings by customers
Induces water savings when prices increase with used volumes
Helps people to appreciate the water supply, including giving water a social value
Requires well designed price structure to be socially
Reduced volume of non beneficial water use
Induces positive water conservation behaviour of customers
More water is available to satisfy the demand
Requires appropriate
technologies High
Maintenance Prevents equipment and conduit failures
Minimises system water losses
Supports good service
Improves the hydraulic performance of the network
Helps prevent system failures
Prevents contamination
Makes the customer responsive to water conservation policies
Gives confidence to the customer to adopt water saving practices
Conserves good quality water to uses requiring such quality
Implies wastewater treatment
Effective water reuse for non human and outdoor recreational uses
Very high investment costs
Higher operation costs than for a single line distributor
Requires the involvement of the users
Create a framework for adopting water conservation and saving
Enforce restriction policies when drought increases scarcity
Favours connections with public water authorities
Favour the adoption of water saving devices and practices
Create public awareness of water conservation
Promote the adoption of water saving practices and devices by customers and the population
Require well planned and co-ordinated efforts of public authorities, schools, water companies and
municipalities
High
Produces data to evaluate operation, maintenance and management programmes and to support a system of information and control.
Supports planning of water conservation measures, and establishment of drought preparedness plans and real-time drought mitigation operational and managerial plans.
Despite advantages, there is a limited use of the metering data when appropriate databases are not installed and used. To fully explore the benefits of metering and monitoring urban water supply systems, it is advisable to make meter data collection, handling and analysis part of an information system, which should also include the production of control, operation, maintenance and management reports. Automation of meters enables the data collected to be transmitted in real time to the information centre, thus to be processed and analysed also in real time.
8.3.3. Metering at customers outlets
Metering the water delivered to customers is essential for billing, to reduce water use and, when a water savings price policy is enforced, to induce customer water savings. Arreguín (1994) reports that billing for the volumes of water used induces by itself a reduction in use of up to 25% in areas that previously had no metering. However, as shown in a study by the Mexican Institute of Water Technology referred by Arreguín (1994), the upper and lower socio-economic classes were generally not responsive to metering, while the middle classes reduced water use by up to 50%.
Metering customer water use has the following main advantages:
Customers pay for the used volumes, which is far better than to be billed by any other criterion
Customers, mainly those of the middle class, tend to reduce water use when they realise that excess water use has a cost
Water savings by the customers provide for improved use of the resources available, thus for better service.
It is relatively easy to fix the water price to cover the full costs of operation, maintenance and management, and thus to improve both the network and the water service, and to provide for avoidance of health hazards
Information on metered volumes provides an accurate knowledge of consumer use patterns, which are important for planning system developments and modernisation, as well as water conservation and water saving programmes, particularly under drought conditions.
Implementing a metering system requires appropriate planning, from the installation stage through the maintenance phase. Meters with the appropriate capacity should be used.
The use of undersized meters leads to false readings and a shorter service life as a result of excessive wear on its components. Conversely, using an oversized meter implies a higher initial investment and less accurate readings of low flow rates.
Although the ideal is to meter 100 % of all residential outlets, this is not always possible owing to the installation costs of a metering system. Studies carried out in various Mexican cities by the Mexican Institute for Water Technology, as reported by Arreguín (1994), have shown that 10 % of the meters installed account for 51% of the total volume used, taking only
major consumers into account. The next 10 % meters account for about 14% of the volume measured, while the last 10 % concern only 3% of the total volume. It is estimated that if 30%
of the residential customers are metered, as much as 75% of the volume can be measured.
Strategies for the installation of meters when capital investment does not allow for metering all the customers can thus be defined as follows (Arreguín, 1994):
Selective metering. Once the major consumers are identified they should be metered first, then continuing the metering process until the target level for the locality is reached.
Metering by sectors. This option involves metering groups of users having similar consumption patterns and dividing the cost of the water used among them.
Combined metering. This is a combination of the two systems above, which is applicable when water use is differentiated. A sector meter can be installed at the upstream end of each sector and individual meters are installed for major consumers.
The water use of the non-metered users can be estimated by difference.
8.3.4. Maintenance of urban water supply systems
Maintenance may be preventive and reactive. It plays a major role in water conservation. The main purpose of preventive maintenance is to ensure the proper functioning of the water supply system, from the upstream water sources to the customers. Consequently, it includes the network reservoirs and conduits and respective equipment, the pumping stations, the water treatment plants, and the metering system. For the latter, meter readings need to fall within a well-defined range of accuracy. A study in Mexico reported by Arreguín (1994) has shown that 23.4% of the meters over-recorded water use, 71.4% under-metered and only 5.2%
measured accurately.
Each utility and sector should have its own program of maintenance. Computer programs may be helpful in establishing and controlling maintenance programmes. Reactive maintenance needs to occur as required. Reactive maintenance takes place in response to information provided by the field personnel, meter readers and users about system failures, equipment disrepair, and inaccurate meter readings.
8.3.5. Leak detection and repair
System losses in urban drinking water supply systems are mainly due to evaporation and seepage in storage and regulation reservoirs, and leaks in water treatment plants, in distribution networks and in home outlets. The used volumes not metered due to inaccurate or non-existent metering, the unauthorised outlets and the unrecorded volumes used by municipal services, such as for watering public gardens or used from fire hydrants, are often accounted as losses, despite the fact that they constitute beneficial uses. Also often accounted as losses are the leaks in households. Summarised in Table 8.5 are the results of another Mexican study covering 15 large cities. It shows that leaks in the system and through the outlets are very high, far larger than leaks in households. However, reported leaks in the network are low, much below what is detected by careful monitoring, particularly in old systems. Leaks in the network are generally higher in systems that breakdown very often.
TABLE 8.5. Results of the evaluation of the water losses in 15 large cities in Mexico (Arreguín, 1994) Taps with leaks Volume lost
through outlet leaks
Volume lost at
network level Volume not accounted due to under measuring
Total losses in system Average
(%)
15 26 10 2 38
Range (%) 5-38 14-59 1-26 0-14 24-60
Leaks in the supply network may be visible or not. Water rising through the soil or pavement provides a visual indication, but it is common to have invisible leaks where the water flows into the drainage system or to an aquifer.
The causes of leaks vary, depending on the geotechnical soil characteristics, quality of construction, materials used, particularly in joints and at valve locations, flow pressure and pressure variation, age of the network, water chemistry, and operation and maintenance practices. Leaks can result from crosswise or lengthways cracking of the conduits, being caused by surface vibrations, poor construction, fatigue and manufacturing flaws of the material, or sudden pressure variations due to fast manoeuvring of valves. Other causes include rusting, poor pipe joints or valve failure.
In home outlets, faults can be due to fissures, perforations, and cuts or loose fittings.
These are due to poor quality materials, poor construction; and external loads.
Leak detection and repair is beneficial to reduce:
system water losses, i.e. the non beneficial water use fraction,
energy consumption, wear of equipment, and operational costs,
contamination risks of the network,
negative impacts of the percolating water.
Leak detection and repair is also beneficial to better utilise the available resource and to facilitate the promotion of citizen awareness in water conservation. That activity may be performed easier with help of models, which support the analysis of a drinking water system (Arreguín, 1994). Descriptive analysis models provide an initial understanding of the system, including the analysis of records of operations, failures, and repairs undertaken, so making it possible to estimate the percentage of losses in the network and in home outlets in the different sectors of the system. Predictive models are based on the knowledge of the age of the network, the materials used, rate of corrosion, most frequent kinds of failures and respective repair to predict the behaviour of the network and its losses. Physical analysis includes fieldwork to detect leaks in the distribution network, home outlets and any other part of the system.
Several leak detection methods exist including: (a) the acoustic method, based on the fact that leaks under pressure produce sounds that can be detected by using appropriate sensors, amplifiers and headphones; (b) the so-called Swiss method consisting of injecting water under pressure into a reach or a sector of the network and measuring the amount of water required to keep the pressure constant, where the resulting volume equals the amount of water leaked; (c) the correlation analyser method which is based on recording the noise produced by a leak using sensors placed up- and downstream of it and then processing the two signals by a correlation analyser to give the respective distances to the leak location; and (d) the tracing method, where tracers are injected upstream and then the leak site is detected with
support of chemical or radioactive tools (Garduño and Arreguín, 1994).
8.3.6. Water pricing
Historically, in most countries, water costs have largely been or still are subsidised. In others, water is supplied free. It is of importance to establish rate policies that emphasise greater user involvement in water conservation and saving. When users are charged appropriately for water services, the water use as well as the water waste tends to decrease.
Water pricing can help to save water if the price structure meets some essential conditions:
prices must reflect the actual costs of supply and delivery to the customers to ensure the sustainability of the water supply services and the maintenance of conduits and equipment;
the price rate should increase when the water use also increases to induce customers to adopt water saving and conservation;
different price rates should be practiced for diverse types of water use in municipal supply, e.g. differentiating domestic indoor uses from gardening water uses; when water is more scarce than usual, prices for less essential uses could be modified earlier;
differential increases in price must be large enough to encourage water savings;
prices must reflect the quality of service, i.e. poor and non reliable service cannot be provided at high cost but costs must change as soon as service is improved.; and
any change in pricing must be accompanied by information and education programs that support an increased awareness of the customers of the value of water and water supply services.
Water benefits are different for each type of user. In urban areas there are several types of water use: domestic, public, industrial, commercial, services, construction, and recreational. Each of these categories reacts differently to the same financial spur in charging for the service, so it is important for the rate structure to be properly designed (Arreguín, 1994). This involves knowledge on trends in costs and the respective price structure, on trends in the water market including its seasonal variations, and information on users' categories and their ability to pay. Other variables that affect decisions are the policies on subsidies and on fines and penalties for water misuse and abuse.
Users must be billed correctly and informed of the amount of their consumption.
Increases and adjustments in prices must be clearly linked with the costs of water services. If they are not prices may become subject to external influences (e.g. the need to raise tax income) and fail to be accepted by the customers. In such a case the customers may react negatively to water saving programmes. Therefore, the political authorities and the users must be clearly informed of why changes are needed, through information campaigns that target the different categories and social sectors, explaining the facts simply and honestly.
8.3.7. Regulation and control equipment
Important progress in design and equipment for urban water supply systems has been made during the last decades. However, investment costs still are high limiting the adoption of respective developments, mainly in less developed areas, where funds are limited but population growth is very high. Particular attention must be paid to the adoption of
appropriate regulation and control devices in the network because this equipment plays a fundamental role for the quality of service, and therefore in the implementation of water conservation and water saving programmes. This equipment mainly relates to:
support appropriate hydraulic functioning of the network, including the avoidance of sudden variations in pressure due to the manoeuvre of gates and pumping stations in relation to variations in demand, which could damage conduits and equipment,
prevent system failures,
prevent the contamination of the network,
provide for flexibility in operation,
maintain adequate service pressure, mainly when the network covers areas with less favourable topography, with large variations in elevation.
The adoption of advanced regulation and control equipment is difficult for small networks and for more remote areas because it requires appropriate technical staff, and investment and operation costs are high.
8.3.8. High service performance
A water supply company may have good water metering, pricing and billing systems but fail
A water supply company may have good water metering, pricing and billing systems but fail