Chapter Nine: Distribution System
- 1 Chapter Nine: Distribution System
- 1.1 Issues Causing Problems in the Distribution System
- 1.2 Operational Schedule
- 1.3 Management of Events of Water Shortage
- 1.4 System Surveillance
- 1.5 Maintenance Schedule
- 1.6 Activities in Maintenance Schedule
- 1.7 Preventive Maintenance Schedule
- 1.8 Leakage Control
- 1.9 Cross Connections
- 1.10 Plumbing Practices for Drinking Water Supply
- 1.11 Chlorine Residual Testing at Consumer End
- 1.12 Sample Records to be Maintained by the Water Supply Utility
- 1.13 Record keeping
1 Chapter Nine: Distribution System
The overall objective of a distribution system is to deliver safe drinking water to the consumer at adequate residual pressure in sufficient quantity at convenient points and to achieve continuity and maximum coverage at affordable cost. Normally, the operations are intended to maintain the required supply and pressure throughout the distribution system. Critical points are selected in a given distribution system for monitoring of pressures by installation of pressure recorders and gauges.
1.1 Issues Causing Problems in the Distribution System
(a) Intermittent System
The distribution system is usually designed as a continuous system but it is often operated as an intermittent system in many supply areas. Intermittent supply creates doubts in the minds of the consumer’s about the reliability of water supply. During the supply period, the water is stored in all sorts of vessels for use in non-supply hours, which might contaminate the water. Often, when the supply is resumed, the stored water is wasted and fresh water again stored. During non-supply hours, polluted water may enter the supply mains through leaking joints and pollute the supplies. Further, this practice prompts the consumers to always keep open the taps of both public stand posts and house connections leading to wastage of water whenever the supply is resumed. Intermittent systems and systems which require frequent valve operations are likely to affect equitable distribution of water mostly due to operator negligence.
(b) Non-Availability of Required Quantity of Water
Failure of source or failure of power supply may cause reduced supplies. Normally, the distribution affected reservoirs are designed for filling in about 8 hours of pumping and whenever the power supply is the pumping hours are reduced and hence the distribution reservoirs are not filled up leading to reduced supply hours and hence reduced quantity of water.
(c) Low Pressure at Supply Point
Normally peak demand is considered ranging from 2 to 3, whereas the water supply is given only for a different duration, leading to large peak factors and hence affecting the pressures in the distribution system. This is common with most water supply systems.
(d) Leakage of Water
Large quantity of water is wasted through leaking pipes, joints, valves and fittings of the distribution systems either due to bad quality of materials used, poor workmanship, and corrosion, age of the installations or through vandalism. This leads to reduced supply, loss of pressure and deterioration in water quality.
Maintenance of appropriate positive pressure at all times to all consumers is the main concern of O&M. Negative pressure can cause contamination of water and very high pressure damages the pipelines. Low pressure may be avoided by taking the following steps:
(i) Purposefully or accidently, a line valve is left closed or partly closed or blockage due to any material causing loss of pressure,
(ii) Too high velocities in small pipelines,
(iii) Low water level in SR,
(iv) Failure of pumps/Booster pumps (either due to power failure or mechanical failure) feeding the system directly.
(e) Unauthorized Connections
Illegally connected users will contribute to the reduction in service level to authorized users/ consumers and deterioration of quality of water. Sometimes, even legally connected users draw water by sucking through motors causing reduction in pressures.
(f) Extension of Service Area
Due to extension of service area without corresponding extension of distribution mains, the length of house connections will be too long leading to reduction in pressures.
(g) Age of the System
With age, there is considerable reduction in carrying capacity of the pipelines due to encrustation. In most of the places, the consumer pipes get corroded or precipitates and leaks occur resulting in loss of water and reduced pressure and pollution of supplies
(h) Lack of Records
Records of replacement of fittings/pipes/valves, scouring of entire distribution system, system maps, designs of the network and reservoirs and historic records of the equipment installed in the distribution system are often not available, whereas some minimum information is required to operate and maintain the system efficiently.
1.2 Operational Schedule
1.2.1 Mapping and Inventory of Pipes and Fittings in the Water Supply System
Availability of updated distribution system maps with contours, location of valves, flow meters and pressure gauges or taping points is the first requirement for preparation of operation schedule. The agency should set up routine procedures for preparing and updating the maps and inventory of pipes, valves and consumer connections. The maps shall be exchanged with other public utilities to contain information on other utility services like electricity, communications etc. 9.2.2 Field Survey and Distribution Network Simulation
Existing maps are used or conventional survey is employed for preparation and up-dating of maps. As an alternative to traditional survey and map preparation, 'total station method is gaining popularity. Total station instruments can be used for survey and mapping of villages where data is not readily available.
The use of modern databases such as Geographical Information Systems (GIS), more and more detailed information can be included in analyses, specifically for monitoring of the network operation and maintenance. This is particularly very useful in cases where there is a huge amount of data and scenarios where manual/hardcopy analyses are not easy to handle or to understand properly.
The use of GIS coupled with Global Positioning System (GPS) in water distribution system management can also greatly enhance the amount and accuracy of data available. The GIS maps are becoming readily available and the GIS system can receive any additional information that becomes available after any replacement, connection or disconnection or expansion of the system has taken place. In this way, these maps enable multiple use: providing direct input for the computer model (hydraulic), accurate billing information and the location of system components that are malfunctioning and have to be repaired, etc.
Evaluation of Hydraulic Conditions
A continuous evaluation of the hydraulic conditions of the water supply system can be done by the O&M personnel after obtaining the data on water volumes in the reservoirs, flow meter readings from and into the reservoirs connected to a transmission system and compared with the expected performance. This evaluation shall lead to identification of operational problems and/or system faults. Depending on the type of problems actions have to be initiated to ensure that the system functions as per the requirement.
Simulation of Distribution Network
Operations have to be planned for specific circumstances such as failure at source, failure of pumps, leakages or bursts. Criteria have to be determined on the basis of analysis of the effects of particular operations on the hydraulic configuration of the water supply transmission system. These effects can be seen in simulated operating conditions. Mathematical simulation models can be developed from basic data on the network such as length, size, flow, characteristics of pumps, valves, reservoir levels etc. This approach can be very useful for analysing the effects of variables on large and complex water supply transmission and distribution systems.
1.2.2 Routine Operations of the Water Supply Distribution System
The efficiency and effectiveness of a water supply system depends on the operating personnel's knowledge of the variables that affect the continuity, reliability, and quantity of water supplied to the consumers. The operational staff should be able to introduce changes in the hydraulic status of the system as required depending on those variables promptly and effectively. Routine operations shall be specified which are activities for adjusting the valves and operation containing procedures for operating the distribution system. It should contain procedures to obtain, process, and analyze the variables related to water flows, pressures and levels as well as the consequences of manipulating control devices, such as operation of valves and/or pumps so that the hydraulic status of the system can match the demand for water. When operators change their shifts, information on valve closure and opening must be exchanged.
1.2.3 Operations in Break Downs and Emergencies
Operations other than routine i.e. during breakdowns and emergencies have to be specified and should be carried out in specific circumstances when normal conditions change i.e. when flows, pressures and levels and operation of pumps change.
1.2.4 Measurement of Flows, Pressures and Levels
It will be necessary to monitor regularly operational data concerning flows, pressures and SR levels to assess whether the system is functioning as per requirements. Analysis of data may reveal overdraw of water to some reservoirs and or bulk consumers. At such places, appropriate flow control devices may be introduced to limit the supplies to the required quantity. A list of priority points in water supply system have to be identified such as installation of meters to measure flows, pressures and levels. A detailed map showing location or each measuring point has also to be prepared. The degree of sophistication of the devices used at each measuring point with regard to indication, integration, recording, transmission and reception of data depends mainly on the skills of the O&M personnel available with the agency and affordability of the agency.
1.2.5 Sampling for Quality of Water
The agency operating the water supply system is charged with the primary responsibility of ensuring that the water supplied to the consumer is of an appropriate quality. To achieve this objective, it is necessary that the physical, chemical, bacteriological and microbiological tests are carried out at frequent intervals. Samples should be taken at different points on each occasion to enable one to make an overall assessment. In the event of epidemic or danger of pollution, more frequent sampling may be required, especially for bacteriological quality. For each distribution system, a monitoring programme has to be prepared showing the location of sampling points. Based on historic records of a system it will be possible for the manager of the system to decide locations for bacteriological sampling and residual chlorine testing. Reference can be made to Section 220.127.116.11 item (ii) and MoW guidelines URT (2018).
1.3 Management of Events of Water Shortage
The objective of developing a programme for managing in times of shortage of water is to reduce the excessive use of water particularly when the source is limited due to the adverse seasonal conditions. Basically, it involves ensuring that a water conservation policy is developed and implemented among water consumers. The following activities can be considered while formulating such a water management project:
(a) Installation of accurate water meters and establishment of a realistic tariff structure to encourage water conservation and prevent wastage of water. Common customer meter chambers can be useful as they assist to minimize tempering of individual/house connection meters,
(b) Introduction of restrictions on use of flushing, showers and other household fittings,
(c) Introduction of devices to limit water consumption in flushing of toilets,
(d) Enforcement of restrictions on use of treated water for watering lawns, cooling, construction, washing of vehicles, etc.,
(e) Encouragement and/or enforcement of the reuse of treated industrial effluents and wastewater,
(f) Development and implementation of public education programmes to encourage water conservation,
(g) Limit of length of service lines (house connections) is usually made as short as practically possible depending on how far is the distribution main.
1.4 System Surveillance
Surveillance of distribution system is done to detect and correct the following:
(a) Sanitary hazards,
(b) Deterioration of distribution system facilities,
(c) Encroachment of distribution system facilities by other utilities such as sewer and storm water lines, power cables, telecom cables etc. and
(d) Detecting and correcting damages of the system facilities by vandalism.
1.5 Maintenance Schedule
(a) A maintenance schedule is required to be prepared to improve the level of maintenance of water distribution networks and house connections through improved co-ordination and planning of administrative and field work and through the use of adequate techniques, equipment and materials for field maintenance,
(b) The schedule has to be flexible so that it can achieve team action with the available vehicles and tools,
(c) Co-ordination of activities is required for spares and fittings, quality control of materials used and services rendered,
(d) Training of maintenance staff shall include training to achieve better public relations with consumers apart from the technical skills.
1.6 Activities in Maintenance Schedule
Following activities are to be included in the schedule:
(a) Establishment of procedures for setting up maintenance schedules and obtaining and processing the information provided by the public and the maintenance teams,
(b) Formation of maintenance teams for each type of service with provision for continuous training,
(c) Establishment of repair procedures for standard services,
(d) Specification of appropriate tools,
(e) Allocation of suitable transport, tools and equipment to each team,
(f) Establishment of time, labour and material requirement and output expected; time required and other standards for each maintenance task, and
(g) Monitoring the productivity of each team.
1.7 Preventive Maintenance Schedule
A preventive maintenance schedule for servicing of valves and maintenance of valve chambers, maintenance of the pipelines: may include the tasks, set priorities, issue of work orders for tasks to be performed, list of scheduled tasks not completed, record of when the tasks are completed and maintaining a record of tools, materials, labour and costs required to complete each task.
1.8 Leakage Control
Wastage of water in the system and distribution network occurs by way of leakage from pipes, joints & fittings, reservoirs and overflow from reservoirs & sumps. The objective of leakage control programme is to reduce the wastage to a minimum and minimize the time that elapses between the occurrence of a leak and its repair. The volume of water lost through each leak should be reduced by taking whatever action technically and economically feasible to ensure that the leak is repaired as quickly as possible. To achieve this, the organization shall prescribe procedures for identifying, reporting, repairing and accounting for all visible leaks.
It will be beneficial for the water utilities or authority or RUWASA if the procedures involve the conscious and active participation of the population it serves apart from its own staff. The management has to process the data and evaluate the work on detection and location of leaks and for dissemination of the results and initiate actions to control the overall problem of water loss. Interim measures for reduction/control of leakage can be initiated by controlling pressures in the water distribution system where feasible.
1.8.1 Leakage Through House Connections
Leakage can be controlled at the point of house connection and in the consumer pipe by adopting correct plumbing practices and improving the methods used for tapping the main and giving house connection and strict quality control on the pipe material used for house connection. An analysis of leaks in house connections and investigation of reasons for leaks in the house connections shall be carried out to initiate action on reducing the leakage through house connections.
1.8.2 Procedures for Detecting Visible Leaks
The water supply utility or authority or RUWASA has to establish procedures whereby the population served by the agency notifies the visible leaks. The water supply staff can also report visible leaks found by them while carrying out other works on the water supply system. Water supply utility or authority or RUWASA has to establish procedures for prompt repair of leaks and for attending efficiently and accurately to the leaks. Critical areas where leaks often occur have to be identified and appropriate corrective measures have to be implemented. Effective use of SCADA should be investigated.
1.8.3 Procedures for Detecting Invisible Leaks
Establishment of procedures for detecting and locating non-visible leaks shall be compatible with the technological, operational and financial capability of the utility or authority or RUWASA. Selection and procurement of equipment for detection and location of leaks must take into account the cost-effectiveness and the financial capability of the organization.
1.9 Cross Connections
Contaminated water through cross connections of water supply lines with sewers and drains is a problem prevailing widely. Intermittent supply further aggravates the problem since, during non-supply hours polluted water may reach the supply mains through leaking joints, thus polluting the supplies. In certain instances, when there are extremely high water demands, the pressures in the supply mains are likely to fall below atmospheric pressure, particularly when consumers start use of pumps with direct suction from the supply mains, a process that is regarded to be illegal.
Regular survey has to be undertaken to identify potential areas likely to be affected by cross connections and back-flow. All field personnel should be constantly alert for situations where cross connections are likely to exist. After identifying the cross connections, remedial measures taken up which can include: providing horizontal and vertical separation between the water main and the sewer/drain providing a sleeve pipe to the consumer pipes crossing a drain, modifying the piping including changing corroded piping with non-corrodible piping, providing double check/non-return valves at the consumer end. The various types of materials of pipe & specifications are being used in the distribution system and specific requirements of maintenance are to be followed as per water supply authority/utility/RUWASA/Manufacturer’s recommendations.
1.10 Plumbing Practices for Drinking Water Supply
The internal plumbing system of the consumer shall conform to the National recommendations and also particularly to the by-laws of concerned water supply authority/utility/RUWASA. The various types of plumbing materials are being used and require different maintenance practices. The utility can regulate up to the connection to supply mains. It is recommended to use licensed plumbers.
Therefore, specific requirements of maintenance are to be followed as per the Manual/ Manufacturer’s recommendations or water supply authority/utility/RUWASA recommendations/specifications indicated in Volume I.
1.10.1 Quality of Pipe Material for House Connection
The water supply authority/utility/RUWASA shall ensure that the connection and communication pipe from the street main up to the consumer premises is laid as per correct plumbing practices and must adopt improved methods for tapping the main. Strict quality control is required on the pipe material used for house connection. The by-laws shall lay down rules for defining the ownership and responsibility for maintaining the point of connection and the communication pipe. In several utilities, the communication pipes are leaking since they are corroded; however these are not replaced by the consumer or by the utility particularly where the O&M responsibility for consumer pipe rests with the consumers.
1.10.2 Contamination through House Connection
While laying the consumer connection pipes there are is a need to avoid contamination of water supplies. This can be achieved by maintaining horizontal and vertical separation between the water supply communication pipe and the sewer/drain. In some instances, a sleeve pipe may be required to be provided to the consumer pipes crossing a drain. It is always recommended to provide a non-corrodible pipe material for the consumer connection. Contamination by possible back flow can also be prevented by ensuring provision of double check/non-return valves at the consumer end.
1.10.3 Rules for Consumer Connections
The water supply authority/utility/RUWASA shall formulate rules for sanctioning of consumer connection, tapping the mains and laying the connection piping. Water supply utility shall undertake inspection of the consumer premises before releasing the connection to ensure that the internal plumbing system of the consumer conforms to the requirements. Water supply authority/utility/RUWASA shall supervise the process of drilling/tapping of the mains for giving connection and laying of the consumer piping.
The process of submission of applications for connections by consumers and carrying out the connection work through licensed plumbers is also prevalent in some utilities. In such cases, the water supply authority/utility/RUWASA shall formulate procedures for licensing the plumbers including the qualifications to be possessed by the plumber, facilities and tools to be available with the plumber for the work to be undertaken by the plumber. The water supply authority/utility/RUWASA shall closely observe the quality of materials used and works done by him and he should act as per procedures laid down in the bye laws/regulations for approval of the connection works, renewal or cancellation of the plumbers’ licenses or any other requirement depending on their performance or non-performance.
1.11 Chlorine Residual Testing at Consumer End
A minimum chlorine residual of about 0.2 - 0.5 mg/l at the selected monitoring point/ consumer’s end is often maintained to ensure that even a little contamination is destroyed by the chlorine. Hence, absence of residual chlorine could indicate potential presence of heavy contamination. If routine checks at a monitoring point are carried out, required chlorine residuals and any sudden absence of residual chlorine should alert the operating staff to take up prompt investigation. Immediate steps to be taken are:
(a) Re-testing for residual chlorine,
(b) Checking chlorination equipment,
(c) Searching for the potential source of contamination, which has caused the increased chlorine demand, and
(d) Immediate stoppage of supplies from the contaminated pipelines.
1.12 Sample Records to be Maintained by the Water Supply Utility
Sample records to be maintained by the water supply utility are given below for guidance:
(a) Updated system map,
(b) Pressure and flow readings at selected monitoring points,
(c) Persistent low pressure or negative pressure areas,
(d) Age of pipes/quality of pipes,
(e) Pipelines to be replaced,
(f) Presence of undesirable materials,
(g) Water budget for each zone served by one SR,
(h) Number of connections given,
(i) Number of meters out of order
(j) Quantity measured at outlet of reservoir,
(k) Quantity distributed/measured or billed,
(l) Water budget for each zone served by one SR
(m) Source of leaks and persistent leak points,
(n) Status of bulk meters - functioning or not,
(o) Status of consumer meters,
(p) Facilities for repairs of consumer meters,
(q) Number of unauthorized connections,
(r) Residual chlorine levels at the pre-selected monitoring points,
(s) Bacteriological quality of the water sampling points,
(t) Persistent areas where residual chlorine is absent/where water samples are found contaminated,
(u) Record of carrying out repairs on the following:
(i) The pipe line leaks or replacement of pipes,
(ii) Change of gland ropes of the valves in distribution system,
(iii) Record on man hours spent on routine operations in the distribution system in the previous year and the cost thereof.
1.13 Record keeping
(a) To maintain necessary inventory of the materials used and required. Record of total cost of repairs and replacements in previous years along with breakdown of material and labour costs with the amount spent on outside agencies for repairs and replacements,
(b) Replacement of damaged manhole covers,
(c) Record on when the exposed piping was last painted and the cost of materials and labour cost thereof, and
(d) Record of the un-served areas - extension of pipelines- need for interconnection.