Water Distribution System Operation

Encyclopedia of Water

Water Distribution System Operation Mario O. Buenfil Rodriguez

[email protected]

Keywords: distribution, operation, leaks, surge, peak demand, regulation, storage, pressure zones, valves, district metering areas (DMA), complaints, maintenance, surveillance, monitoring, information systems, public relations, disruptions, backflow prevention.

Index:

1 2 3 4 5 6 7 8 9

Operation, maintenance and design of water services Desirable operation conditions Water distribution system elements Principal operations Water delivery and monitoring Prevention and safety Maintenance and repair Public relations and management Recommended bibliography and webliography

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1

Operation, maintenance and design of water services

Contemporary cities and their inhabitants depend on a reliable and generous public water supply system for their functioning, and in order to protect and promote health, productivity and well-being. In fact, the possibility of having piped water and sewerage systems at home is an explanation why cities can support so huge human concentrations. Some mayor technological and cultural changes, to make cities less dependent of such public services, are needed but still far in the future. These vast systems, almost invisible to many as they are underground networks, are complex and delicate arteries that require daily operation and care by professional people devoted exclusively to such tasks. Various and ample are the duties and responsibilities of any water utility; although there are some variants around the world. Some utilities deal exclusively with clean water distribution; while others have broader functions as: extraction from a remote site, conduction, purification, distribution, sewerage, waste treatment; and even tasks as operation of pipe networks for fire combat, or selling treated wastewater; pluvial drainage; solid waste collection; or energy supply. Focusing exclusively on the operational tasks for the distribution of clean water in a city, these involve: monitoring flows, pressures, storage levels and water quality at different network locations; controlling and moving valves; attending reports and enquiries from the public; billing and charging for consumption; keeping updated infrastructure maps and consumers records and census; repairing leaks; replacing or improving pipes, hydrants, pumps and other water distribution network’s components. There is not clear or definite boundary among operational and maintenance tasks; and their distinction is merely on the intensity or frequency of a given job. Sometimes the same employees team perform operational, preventive or corrective maintenance tasks. In contrast, other rather specialised tasks can demand a particular contract with a private service provider (as analysing water samples to detect a specific and difficult pollutant, or controlling and supervising a sophisticated automated pump).

Besides, there is a strong bond between the system’s “hydraulic design” and it’s “operation”, and often can be taken as synonymous. For instance, the control of pressures may be achieved automatically by the proper location of storage tanks or automatic valves. Although in some systems, not so well designed, frequent manual movements (operation) of valves may be needed. The same can be said for the filling and emptying of water volumes in regulating tanks, in order to meet differences in demand and supply flows. When storage tanks are properly sized to convene daily variations of demands with timing of supply pumps, they will function correctly, but if not a lot of toil is required from the “operations personnel” (usually accompanied by uneasiness and complains form consumers). One practical definition of our topic, although not accepted everywhere (and not even here), is this: Operation is the organized procedure for causing a piece of equipment, a treatment plant, or other facility or system to perform its intended function, but not including the initial building or installation of the unit. Usually operation and maintenance are referred simultaneously, as O & M, meaning the management of a facility involving operating, repair and replacement. ________________________________ MW-551 wat-dis-sys-operation pg. 2 of 9

Some other, more general definition (World Bank), states that operation includes the planning and control of the extraction/collection, treatment, conveyance, and delivery of water, and/or the collection, treatment, and disposal of effluent. It also covers the management of client and public relations, legal, personnel, commercial, and accounting functions.

2

Desirable operation conditions

Not all cities attend the same service standards for water quality, pressure, or reliability; although most of them guide their performance and duties by a certain set of local goals or regulations. Sometimes there exist an external autonomous supervisory board, sponsored by consumers, or by an international agency, to guarantee the provider’s accountability in protecting people’s health and economy. Some of these operational goals may be: - Continuity of supply (24 hours, 365 days per year). - Keep low water tariffs (in balance with expenditures and investments), and in an increasing block fashion (the more you consume, the more you pay per water unit; in order to keep the water demand as small as possible and preserve the resource). - Promote and advice customers to keep their water consumption low (demand management). - Pressure not too weak, nor too strong at each house connection (around 10 m to 30 m of water column; this is, between 1 to 3 bars). - Curb water leaks (pipes burst), and when they occur, repair them within few hours. - Satisfy daily and seasonal variations in water demand without spillages or damages to infrastructure, or inconveniences to consumers. - Use the least possible energy for pumping and other processes (low operating costs). - Courteous, fair, and without discrimination treatment to all consumers. - Water quality in all points of the network must meet established standards. - Optimize the use of the system’s installed capacity for water storage, pumping and conduction (profit and utilize existing infrastructure, keep it in good shape, and avoid the need of building more of it).

3

Water distribution system elements

It is convenient that any water supply system be simultaneously involved on, or at least aware of, the sewerage system and the treatment and disposal of wastewater. However, focusing only on the supply side, a water network may depend on the water coming from remote sources, purification plants, aqueducts and pumping stations. All these installations rely on various minor components and devices as: gates, valves, cisterns, filters. All such items require careful operation and maintenance by the same institution attending the distribution network in the city. Sometimes the water sources are within the urban area, as in the case of pumping wells intermingled with the network. In that last case, the water quality and pressure can be assured merely by local additions of chlorine or equivalent, and through booster pumps or pressurebreaking valves or tanks. Some of the elements in a water distribution network are: elevated tanks, underground reservoirs or cisterns, booster stations, valves of different types, meters (for water mains and for customers consumptions), pipes, house connections, various types of fittings and protection cages, fire and public hydrants, local chlorination equipment, monitoring and sampling devices, telemetry and SCADA systems (supervisory control and data acquisition), with all their electronic and ________________________________ MW-551 wat-dis-sys-operation pg. 3 of 9

electric apparatuses and connections, etc. Besides those previous mentioned “fixed” (on-site) elements, there exists a wide range of necessary mobile equipment as vehicles, cranes, winches, mobile laboratories, maintenance and repair equipment, etc. Water distribution pipes are normally arranged in grid or looping designs to provide easy flow to water through different routes (particularly during hours of high demand) and to avoid lines that dead-end and may cause water quality problems. All distribution systems should contain sufficient valving so any area can be isolated for repair, or for scrutiny in case of contamination risk, and only a reduced number of customers be affected during the disruption.

4

Principal operations

Public water systems are designed to provide and maintain a reliable, high-quality water source (e.g. groundwater or surface water). Although one important operation to meet drinking water standards is the water treatment, it will not be covered here in order to concentrate in what happens and is required at the water distribution network. Operations there deal with different cares and purposes, among which is preserving the water quality in the network. The operation of a water distribution system (inevitably linked to its maintenance and design) includes attending all kinds of requests or complaints from customers; meeting local standards and federal regulations; and the upkeep of pipes, storage tanks and pumps that convey the water. Some of the activities are: · Hydraulic performance to meet water demands · Maps control and updating · Modelling and corroboration of system’s hydraulic behaviour · Records (telemetry, samplings), control and analysis · Leak detection and repair · Cross connection control and backflow prevention · Gauging flows (district metering areas, DMA) and consumptions (meters) · Billing consumers and collecting money from them · Exercising of valves · Water pipe flushing and internal cleaning · Water quality monitoring · Chlorination or dechlorination at local points · Water main repair/replacement · Electric and electronic equipment conservation and upgrading · Inspecting quality of materials (pipes, joints, chlorine) and performance of equipment (water meters, valves, etc.) · Storage tank maintenance · Pump maintenance · Prevention and training against vandalism, terrorism or emergency situations (drought, flooding, earthquake, etc.)

It would take too long to give details of all these operations, so only brief comments, for some of them, will be given in the following sections:


5 Water delivery and monitoring Evidently the most important operation of any water distributing system is assuring that enough and timely water arrives to each house. Therefore, one basic operation is the regulation of flows to adapt them to the hours of peak demand (e.g. from 6 am to 8 am), and to those of low demand (e.g. during the night). Usually, in well-designed and developed countries’ systems, these manoeuvres are performed “automatically” through “operational storage” from regulating tanks around the city. These tanks have float or diaphragm actuated valves that close the inflow when full, preventing spillage, and besides can send a signal to halt a remote pump. This exemplifies how operation depends on design, which in poor or simple systems, or in emergencies, has to be done manually. Pumps and valves can be pre-programmed to start or stop at given schedules, and be monitored and acted-on through automatic or semiautomatic computerised supervisory control systems (SCADA), which can check pressures and flows in selected network points. On the other hand, they could simply be controlled manually, according to certain seasonal rules (e.g. rationing of water in drought times). Telemetry and the ability to communicate efficiently are important in the successful operation and maintenance of a complex and expanded water supply system. One option is the use of mobile radiotelephones. Telemetry can provide a complete updated picture of the status of all components in the network, such as reservoir contents, water movements and trends, pump stations. Condition monitoring is part of preventive maintenance, and will help to minimise unscheduled shutdowns and improve reliability of services. Sites operating as unmanned installations require that intrusion and hazard alarms be reported as soon as possible, so that steps can be taken to limit possible damage. Remote operation of pumps, gates, etc. is required to ensure co-ordinated operation of tandem plant and to alleviate staff shortages. Some important and routine monitoring task is reading house meters of all consumers. This will not only give data for billing according with consumption, but also clues about possible leaks in the system, or about clandestine connections, when combined with information of DMA (district metering areas), which is another important monitoring operation. The purpose of these is to have knowledge about volumes supplied and consumed, in order to detect possible money losses, leaks, bursts and wastes; and correct them as soon as possible. Water balances (audits) and statistics will give information to decide if, instead of a local repair, a full pipe replacement is more convenient. Water leaks can be visible, but often they are hidden, requiring specialized equipment and personnel for their location. Continuous surveying and sampling of water qualities and hydraulic parameters (pressure, flow direction, volume supplied) at different locations is an important task. Those records must be compared against written standards, and particular utility’s goals and performance rules. The purpose of that would be to detect failures and correct them, as well as finding opportunities to improve service quality and efficiency, besides utility’s ________________________________ MW-551 wat-dis-sys-operation pg. 5 of 9

revenues, through the design of better operating strategies. In this regard, an important tool is the hydraulic modelling of the distribution system. Hydraulic transients, or surges, occur at rapid flow changes in pressurized water conveying pipelines. Normally such transients (water hammer) are considered a problem as they might damage the pipeline due to strong pressure peaks, subatmospheric pressures or fatigue. Through the use of simulating models, incorporated into hydroinformatic tools, it is possible to assess the existing water distribution systems, in order to suggest a more efficient hydraulic performance and propose rehabilitation strategies. 6 Prevention and safety Many operational tasks could be classed as related to “prevention and safety”. Some of them, as leak detection and control, or water quality sampling, already have been mentioned. Some others are cross connection control, backflow prevention, and protection and vigilance against vandalism or emergency situations. Continuous positive pressure is necessary in all distribution systems to prevent creating a vacuum in the water-supply main. These vacuums can lead to back siphonage with possible contamination or even collapse of the pipe sections. Cross connection control and backflow prevention are operational programs that both, the utility and its customers, must implement to prevent contaminants and non-potable water (e.g. wastewater, storm water, process water) from being drawn into their drinking water system. Backflow typically occurs when distribution system pressure drops due to a water main break or due to fire fighting demands. It has two interpretations: a) a flow condition, induced by a differential in pressure, which causes the flow of water or other liquid into the distribution pipes of a potable water supply from any source or sources other than its intended source; b) the backing up water through a conduit or channel in the direction opposite to normal flow. Cross connections are physical, piped connections between potable water and an unsafe, or polluted water source. They threaten water quality and public health through the backflow of such hazardous substances as antifreeze, boiler water, and sewage. Cross connection control operation, besides building codes and regulations to avoid them, consist on inspection routines, and checking backflow prevention devices on particularly high-risk service connections (e.g., a wastewater treatment plant). Numerous recommendations, cares and routines can be implemented concerning general protection and vigilance against vandalism or emergency situations. Their selection and adoption depend on the risks, characteristics of the utility and infrastructure, and even the present or expected climate and political and socio-economic atmosphere. Some examples are: Lock all doors and set alarms at offices and main installations. Limit access to facilities, especially to water supply reservoirs. Secure hatches, meter boxes, hydrants, manholes and other access points to the water distribution system. Control access to computer networks and control systems. Write and periodically review security and emergency plans, and train employees frequently. Assess the vulnerability ________________________________ MW-551 wat-dis-sys-operation pg. 6 of 9

of water sources, drinking water treatment plants, distribution networks, and other key infrastructure elements. Improve computer system and remote operational security.

7 Maintenance and repair It is important that all network valves be operated periodically, merely to ensure their proper performance when really needed. A dead-end line must be flushed frequently or the customer on that line will be served poor quality water. Water pipe flushing is a preventive maintenance task intended to preserve the hydraulic characteristics of the pipe, besides the quality of the water flowing trough it. It removes any accumulated sediments or other impurities deposited in the pipe. Flushing is performed by isolating sections of the distribution system and opening flushing valves or more commonly fire hydrants to cause a large volume of flow to pass through the isolated pipeline and suspend the settled sediment. Water mains may also be mechanically cleaned through the use of swabs or pigs which are devices that are pulled through a section of line that scrape the accumulated debris off the inside of the pipe. The major environmental aspect of water pipe flushing is the discharge of flushed water, which may be high in suspended solids and other contaminants that can harm water bodies. The negative impacts of the discharge may be minimized by discharging the flush water into a sanitary sewer with adequate capacity or by discharging the flush water into a separate storm sewer system, preferably with management measures such as a detention pond, where solids can settle before the water is discharged. Repair or replacement of water mains must be performed frequently to correct or substitute broken, corroded, or leaking sections of pipe. Either the broken pipe section is replaced or, as is often the case, a repair sleeve is placed around the outside of the broken pipe section and clamped into place. Following the pipe repair, the line is typically flushed and then disinfected with a chlorine solution. The chlorine solution is usually mixed on site with powdered calcium hypochlorite or sodium hypochlorite. Pipe repair and replacement could affect the environment (erosion of soil, sediments, high concentrations of chlorine, etc.), and such impacts should be minimized through control measures. Storage tanks require frequent inspection and maybe occasional repairs. The most frequent repairs are repainting of walls and replacing screens over vents and other points of access to insects, birds and rodents. Steel tanks are subject to corrosion, which is prevented by painting them on a regular basis. Pump maintenance must be performed to ensure booster and other distribution pumps stay in working order. Their maintenance involves frequent inspection and tests for excessive vibration or noise, providing grease and lubrication regularly and checking the pumps bearings and packing glands.


8 Public relations and management Operation of a water distribution system have much to do with the management of client and

public relations, legal, personnel, commercial, and accounting functions. To be sustainable, an operation must be financially viable. Because of the pressure to expand the area served, viability generally implies the recovery of the costs of operation and maintenance, as well as capital costs. Public utilities often have difficulty getting approval for increasing their charges to levels that are financially and economically adequate. Sometimes this is for political reasons but often it is also because the requests are poorly prepared and their urgency is not well perceived. Higher charges must be justified not only to the parent entity but also to consumers. Public relations campaigns can be helpful here, but quality service is often crucial to securing consumers' acceptance of increases. Demand management, in order to keep water needs low and congruent with the natural local resources is a vital task. For this purpose the education campaigns directed to the public, the installation and reading of water meters, the appropriate an fair setting-up of water tariffs, the proper operation and location of consumers information and attention modules (telephone, internet, direct presence) are basic. Employees must be trained and aware of their role in transmitting correct information and messages to the public. 9 Recommended bibliography and webliography - ABPA, “Recent Backflow Incidents and Articles”, American Backflow Prevention Association http://www.abpa.org/

,

http://www.abpa.org/incidents.htm

- AWWA, “Water Distribution Operator Training Handbook”, American Water Works Association, Denver, USA : AWWA, 1976 http://www.awwa.org/wdoth.htm - Chase Don, Savic Dragan, Walski Tom, “Water Distribution Modeling” Haestad Methods Inc. http://www.haestad.com/library/books/wdm/authors.asp

- CIWEM, “Water Distribution Systems. Water practice manual 4”, The Chartered Institution of Water and Environmental Management, CIWEM (formerly Institution of Water Engineers and Scientists, IWES), 1984 http://www.ciwem.org.uk/publications/manuals/index.asp

- Environment Canada, “The management of water”, National Water Issues Branch, Environment Canada, 1998 http://www.ec.gc.ca/water/en/manage/e_manag.htm

- EPA, Environmental Protection Agency, USA, “Recommendations to Improve Security at Drinking Water Facilities” 2001 http://www.lgean.org/html/whatsnew.cfm?id=259 - Greater Vancouver Regional District Drinking Water Treatment Program, “Best Management Practice for Pigging and Flushing Water Mains” , 1997 http://www.gvrd.bc.ca/services/water/chlorlin/flushing.pdf - Hawken Paul, Lovins Amory, and Lovins L. Hunter “Aqueus Solutions”, Chapter 11 of book “Natural Capitalism: Creating the next industrial revolution”, Rocky Mountain Institute http://www.natcap.org , http://www.natcap.org/images/other/NCchapter11.pdf http://www.rmi.org/sitepages/pid172.php , http://www.rmi.org/images/other/W-AqueousSol.pdf

- Havlik V., “Solution of water supply and distribution networks”, Danish Hydraulic Institute (DHI), http://www.dhisoftware.com/mikenet/Download/Papers/hague97.pdf

- James, William, “Urban Water Systems” Guelph University, Canada. 1999 http://www.eos.uoguelph.ca/webfiles/james/homepage/Teaching/661/wj661Modules.html

- James, William, “Hydraulics and hydrology vocabulary”, Web Manual. U. of Guelph, Sch of Eng'rg., 1996 http://www.eos.uoguelph.ca/webfiles/james/homepage/stillunclassified/wjvocab.html

- Jönsson Lennart, “Hydraulic transients as a monitoring device”, Department of Water Resources Engineering, University of Lund, Sweden , IAHR , International Association of Hydraulic Engineering and Research http://www.iahr.org/membersonly/grazproceedings99/doc/000/000/110.htm

- Kenneth Kerri, “Water Distribution System Operation and Maintenance”. -- 3a. Ed. -- Sacramento : California Department of Health Services, EPA, 1994. 514 ; ISBN 1-884701-16-7 http://www.owp.csus.edu/WDS.html ________________________________ MW-551 wat-dis-sys-operation pg. 8 of 9

- LGEAN, Local Government Environmental Assistance Network, “Water Distribution System Operation and Maintenance” http://www.lgean.org/html/lgo/WTRSPPLY-01.html - Mays Larry W. “Water Distribution System Handbook” AWWA American Water Works Association, 1999, McGraw-Hill Professional Publishing, http://www.amazon.com/exec/obidos/ASIN/0071342133/002-30750600220023

- OIEAU, Office International de l’ Eau (International Office for Water) “Overview of Training Services”, France, http://www.oieau.fr/espagnol/stages/smt97.htm#1997_4 or 1998 http://www.oieau.fr/english/stages/smt97.htm#1997_4

- University of Florida “Backflow/Cross-Connection Control Program” http://www.dep.state.fl.us/water/drinkingwater/bfp.htm , http://www.TREEO.ufl.edu/backflow/

- World Bank, “Managing Urban Water Supply and Sanitation: Operation and Maintenance”, GDRC, Global Development Research Center, http://www.gdrc.org/uem/water/wb-urbanwater.html
