|Operation and Maintenance of Water and Sewerage Systems (Ministry of Water - Tanzania - Rwegarulila Water Resources Institute, 1999, 90 p.)|
|A. Maintenance of Water Supply Units Principles and General Procedures|
The problems of planning, design, and construction of water supply systems are usually slight when compared with the problems of operation and maintenance of the systems, after they have been constructed.
The situation is aggravated by the glamour attached to new construction and the greater importance given to expenditures for new construction in contrast to expenditures which are necessary for operation and maintenance.
Once the units have been constructed, it is necessary to ensure that they have lasting reliability and will continue to function as intended.
The basic requirements for this are that the units have been constructed properly and that they are kept in a state of good maintenance.
1.1 The Problem
Cracks in masonry or concrete, leaky covers, damaged or defective pipes, vents, screens, etc., facilitate the entry of ground water and/or surface water and small animals which will contaminate the water and cause health hazards. Water will be lost as a result of cracks, leaky pipes, untight pipes passages through walls, etc. and joints. Metal parts rust. Corrosion leads to loss of water and contamination. Sediment can cause blockages, and affects the yields of wells and springs.
Valves not functioning properly will impede operation and cause loss and contamination of water. Clogged intakes, sand traps and screens do not only affect the proper functioning of the units and equipment, but they can also lead to contamination of the water and damages to equipment.
The water tight backfill can be damaged by excavations or by deep cracks in the soil; thereby allowing surface water to enter into the system and to cause health hazards. In the long-run the safety of the structure itself can be endangered because of cracks in itself and/or the adjacent ground and as a result of ground water and/or surface water entering through the cracks.
Inadequate operation and maintenance leads to breakdowns involving water loses and interruptions. Water supply interruptions and water loses do not only affect the consumers, but they will also reduce the revenue. Reduction in revenue means less funds for operation and maintenance. This in turn results in inadequate operation and maintenance thereby completing and repeating the cycle of the vicious circle. If money has been borrowed for the construction of the water supply system loan repayment will be in areas; aggravating the situation.
1.2 The Solution
The solution is the execution of a maintenance programme which works.
Maintenance of a water supply unit is based on three considerations.
2. operational; and
Maintenance work must be carried out in time in order to prevent or at least minimize the possibilities of structural damages, interruption of service, contamination of the water and increases in the cost of repairs.
A water supply system is designed and constructed for the purpose of providing an uninterrupted supply of adequate and safe water.
Proper design and construction will ensure that the unit or system will function as intended provided it is operated and maintained properly.
After the construction is completed the system is handed over to people who are responsible for running it. Their work includes operation and maintenance which attempts to ensure that the various components of the system do function as intended and render the desired service.
Operation refers to the performance of activities and use of resources for making a structure, a machine, an equipment, or a system of production do the work it is intended to do. To operate satisfactorily the system and its parts must be in a condition to do their intended work when given the necessary complementary inputs of labour, energy and raw materials.
All types of structures, machinery, or equipment, units, or system of production tend not to do the work that they are intended to do; or not to function at all, unless special efforts are made to maintain them and restore their capacity.
Maintenance mean making periodic inspections which are necessary to determine the extent of this negative tendency, carrying out appropriate remedial measure, and keeping records of the observed deficiencies and the works carried out.
The word maintenance is normally used to describe one of two distinct types of activities: preventive maintenance. The other type is corrective (curative) maintenance.
Preventive maintenance is that which is conducted to minimise malfunctioning, failures or breakdowns; corrective maintenance is that which is carried out after the damage or break down has occurred. A preventive maintenance programme cannot hope to prevent all failures or breakdowns, thus some corrective maintenance will have to be carried out from time to time. A successful preventive maintenance programme will result in less frequent failures and shorter interruptions of service.
The discussion on preventive maintenance in this Module concerns itself with the technical aspects of water supply units.
2.3 Curative Maintenance
Cases of emergency are examples of curative (corrective) maintenance and have to be dealt with as they occur.
The main cause of breakdown or malfunctioning of the unit may or may not be obvious at once. In any case the most obvious measures shall have to be taken immediately followed by systematic inspections in order to make a reliable job. At such inspections representatives of authorities who are concerned with the safety and stability of the structure, the operation of the units, and the quality of the water, should be present if possible.
Inspection consists of checking the physical conditions of a structure and its surroundings.
Inspections are made in order to find out what is missing, gone wrong, or about to go wrong and to decide on the remedial actions that have to be taken.
3.1 Scope of Inspections
The inspections shall be made in order to assess the conditions of the units and determine the steps to be taken to remedy the deficiencies. Thereby, equal emphasis should be placed on the
- operational, and
The conditions will show whether and to what extent the deficiencies adversely affect
- the safety and stability of the structure;
- the proper operation of the unit; and
- the quality of the water.
3.2 Extent of Inspections.
A record should be made of the observed deficiencies.
Water samples should be taken. Notes should be made on the accumulation of sediments, the presence of small animals and the origins of small animals.
The inspection must look out for
- rock pockets (porous, mortar deficient portions of hardened concrete consisting primarily of coarse aggregate and open voids; caused by leakage from formwork, or separation during placement of concrete or insufficient consolidation, or both);
- insufficient bond of screeds and plaster;
- cavities under screeds and plaster;
- roots (these are an indication for cracks and harmful connection with the exterior);
- roofs and covers which are not watertight; porous parts; holes; insufficient cover of the reinforcement steel;
- defective inlet, outlet, overflow, and wash-out pipes;
- defective measuring facilities; and
- blocked vents.
3.3 Types of Inspections
Inspections can be classified according to the times when they are made. It is necessary to distinguish between three types of inspections.
1. Inspections made before putting the unit into operation for the first time;
2. Periodic inspections made normally without interrupting the operation; and
3. Periodic inspection made by interrupting the operations as necessary.
It should be pointed out that even a newly constructed water supply system has to be checked before it is commissioned in order to ensure that it is properly constructed and that it works as intended. This first type of inspection is usually a part of the construction phase.
The more painstaking the construction work, and the more thorough the first inspection and the ensuing corrective work the less will be the trouble in the life of the structure as far as the structural condition is concerned.
This first and most important inspection is the inspection which is made after the completion of the construction work and before the unit is put into operation for the first time. This inspection and the remedial work which follows it are the basis for a sound structure which will function provided it is properly maintained and operated in the future.
The team which was involved in the construction should not make the inspection by itself. The most appropriate members of the inspection team ought to be persons who would be responsible for the operation and maintenance of the unit or system.
The team which was involved in the construction would itself have made an inspection of the work and carried out improvement works as necessary before announcing that it is ready to hand over the unit which has been completed.
The structures will be inspected by a team whose members represent at least the group which is responsible for the construction on the one hand and the future operation and maintenance on the other hand.
In order to facilitate the work the inspection should follow a systematic pattern using a check list.
A record is made of the inspection and agreement reached regarding the works (if any) which have to be carried out before the unit is put into operation.
The second inspection will verify whether all works agreed upon during the first inspection have been carried out properly.
Tests are made to check the performance of the completed unit.
Water retaining structures including passages of all pipework and fittings which are built - in have to be tested for watertightness.
A record is made of the tests and their results.
4.3 Disinfection and putting into operation
After the successful completion of the works and the satisfactory results of the tests, the units will be cleaned thoroughly and disinfected. Then the units are put into operation.
Structures can be damaged as a result of acts of nature and/or human beings. Damages, caused by human beings can be due to ignorance, carelessness, or abuse.
The physical conditions of the units have to be checked frequently. The frequency depends on local conditions. The type and location of the unit and the available manpower are some of the major factors which govern this frequency.
This is the essential part of preventive maintenance. Inspection of each unit by at regular intervals is necessary for the detection of structural defects and other faults which may develop from time to time either from fair wear and tear or through external conditions such as ground subsidence or abnormal weather. The roadways, pathways, fences and any buildings should also be inspected regularly with the aim of noting defects for repair. Painwork, particularly of steel water tanks should be well maintained throughout the waterworks.
For some of the visual inspections it is not necessary to interrupt the operation. The aim of the inspection is to find any changes or developments in the structure and the surroundings which would adversely affect the safety or stability of the structure, the operation of the unit, and the quality of the water. Basically the inspection concerning the physical conditions is similar to the inspection which is made before the unit was put into operation for the first time. The main difference is that the inspection and the ensuing remedy for the correction of the defects are now the sole responsibility of the maintenance team. However, in cases where major repairs or reconstruction works are necessary a construction team or group can be assigned to carry out the work.
Components of units such as valves, vents, overflow pipes, etc., can be inspected without interfering with the operation of the unit in question.
The periodic inspections may sometimes also require the interruption of the service. They are concerned with the inspection of the interior of all water retaining structures. The interruptions have to be made because the chambers shall have to emptied in order to carry out the inspections and the ensuing necessary works.
Such an inspection will be made once a year, once in two or three years depending on the size of the system, the nature of the unit and the source and quality of the water.
Such maintenance should be made at times when the water consumption is low. Local conditions and experience will indicate the most suitable month of the year or even the day(s) of the week in that month. Even then preparatory work is necessary. All tools and equipment as well as materials and labour should be organised before the chambers are emptied and the maintenance works (= inspection + remedial action + records) started.
When the necessary maintenance does not require a long time, the impact of the interruption of service (if any) will not be too hard on the consumers. In any case the consumers ought to be informed in advance. They shall then be able to reserve some water and to programme their domestic activities. This also minimizes any inconvenience due to repairs which might take time in excess of the average.
Remedial activities of maintenance include
1. Repair, replacement, etc., of parts which are damaged, worn or become obsolete;
2. Removal of unwanted external and internal waste build-up;
3. Application of protective paint;
5. Disinfection; and
6. Public relations and education.
The details of the remedial measures should be laid down in writing. Some persons may be able to carry out the job without such written guidelines. What should be strived at is the cultivation of positive habits both during the training and the actual performance of duties. Only thus it will be possible to ensure that the maintenance work is carried out in a systematic manner.
Records are required to provide information on which future actions can be based.
8.1 Records of the system and extensions
These would include records (such as as-built drawings) of the various units of the waterworks. Instances are not uncommon, where the position of some valve or pipe is known only by one or two persons, usually the oldest employees. Such situations must be corrected.
Each water supply plant should have an up-to-date layout plan of the waterworks. Or units of which the line of every pipe and the location of every valve are clearly marked. Each valve on the plan should be numbered and the number painted on or near the actual valve. Such a plan is particularly useful whenever there is a change of attendant or in cases of emergency. Any extension work is done to the system it should be recorded, preferably with a sketch. These records, if kept in a systematic manner, will provide ease of reference to any portion of the system. Alterations to all works should be recorded also.
8.2 Records of Maintenance
Records of maintenance are very important. They should clearly describe the deficiencies and the remedial measures that have been carried out. Whenever possible, the written descriptions ought to be supplemented with clear sketches.
All happenings affecting the works; actual works carried out, routine or unusual, (occasioned by accidents, breakdowns or other conditions), should be recorded as they occur. Copies of log sheets should be forwarded to the head office.
At least a simple log book or log sheet should be kept at even the smallest works. Any troubles that occur and the date when they are put right should be recorded also. Any sign of wear or damage should be noted in a diary and reported so that spare parts may be obtained on time. Records should also be kept of repairs that are required. The maintenance jobs that must be done at infrequent intervals should be marked in a diary in advance so that they are not forgotten.
From these records isolated and frequent troubles can be pinpointed, an efficient schedule for personnel planned, and estimates for operation and maintenance made with reasonable accuracy.
Further maintenance records will facilitate evaluation and monitoring as well as planned maintenance including the improvement of future design and construction.
8.3 Recording of Information
Any modification, change or improvement in the system, unit, etc., is to be incorporated in the records as it occurs. Information should be recorded as soon as it is obtained and should not be allowed to accumulate. Such accumulation will deter a start. And when a start is made at last, it will prevent a good progress; as there will always be something which is more important or more urgent. Experience shows that recording of accumulated data is doomed to contain mistakes.
8.4 Keeping of Records
An annual report summarizes the records for each water supply system. It helps to assess future maintenance requirements, warns of possible extensions that may be required.
It is also most important to prepare certain special reports which are then distributed to those concerned.
It should be appreciated that it will not be possible to design and implement a maintenance programme which will satisfy all conditions everywhere. An individual schedule must be worked out for each individual system taking into consideration the local conditions. It should be remembered that such a schedule is dynamic and ought to be modified and improved all the time. The reports and records on the system and its maintenance will greatly help in the elaboration of the details for the modification and improvement of the maintenance schedule. A systematic maintenance programme based on records and realistic schedules and provided with the necessary logistics will ensure a reliable service with less frequent breakdowns and shorter interruptions.
9.1 Components of Maintenance Programme
In order to be effective a maintenance programme must have sound
- financial; and
The discussion in this Module deals with the technical aspects only. It should be pointed out, however, that the technical measures cannot be fully realized without the necessary administrative and financial support.
In preparing a maintenance schedule for the first time one should start with a survey of the water supply systems and make an inventory of all components and units of the systems. Details of each unit should be recorded separately on suitable simple forms which could eventually provide a complete history of the unit and thus of the system of which it is a part. In case there are no previous records, the second thing to do will be to complete the records as appropriate where possible.
After the completion of the inventory, the tasks to be carried out and their frequency shall be determined taking into account local conditions and experience. Presentation should be best in tabular form.
The work schedule which may be tabulated should show the work to be done at the prescribed frequency at every location. The individual items can be given reference numbers and the frequencies figures or signs to show whether the tasks are weekly, monthly, quarterly, six monthly, yearly, etc., in order to make the tabulated summaries handy.