WATER LOSSES IN THE DISTRIBUTION NETWORKS
Water distribution network is the most expensive in the drinking water supply system of populated centers (60-80% of the total cost of installation), due both to its large length (2-10 m / capital); and the fact that is a very applied hydrodynamic and static system (it works under pressure and is placed under roadways), and most of the problems concern the relationship between water quality, which is made of materials, their age, operating pressure and water losses.
Aging materials increases the water losses. Today, water losses in the distribution networks, lies on average between 40% and 60%. Water quality is becoming more expensive and less apparent need for an appropriate strategy for achieving optimal system operation so that the overall water and financial resources to be used as rational as possible. Water losses are defined as the difference between the amount of water entered into the distribution system and authorized consumption, component which includes both the apparent and real losses.
Volume of water entered into the distribution system is the annual volume of water entered into the distribution system, consisting of authorized consumption and water losses. Authorized consumption is the amount of water used by registered customers, consisting of authorized billed consumption (measured and unmeasured), bringing the income and authorized consumption invoiced (measured and unmeasured), but without revenue.
Actual losses of water are given annual volume of water lost through all types of leaks (pipeline damage and loss, cleaning tanks and branching) to capture and to the point of metering of consumers. Apparent losses include actual volume of water used by unauthorized consumers (including the use / misuse connection) and measuring equipment data errors. It is recommended that all components of real losses of water to be measured by the best means available. It is important to assess correctly invoiced water because its cost is reflected in the water price. Actual water losses should not exceed 15% for November networks (under 5 years) and 35% for existing networks undergoing rehabilitation and / or extension.
Percentages greater than 35% of water losses are considered anormal and require the adoption of appropriate measures. The amount of water losses in the distribution networks under pressure, given the size of holes and cracks in pipes and fittings, holes due to excessive chlorine corrosion, faulty joints, the mechanical stress from poor execution of the works adjacent ruptures or burglary pipeline caused by water hammer, leaking hydrants, etc… The optimal operation of distribution networks should I place between pmin and pmax = 0.7 bar = 6 bar. Under these conditions may be obtained: the life extension of distribution network infrastructure, reducing the frequency of failures in pipes and connections, reducing the flow at all existing leaks and breakdowns in the system at any time, reducing consumption to users connected directly to network, reducing wastage of water to consumers in the network, waste water, even counted, is also a loss of water. Frequency of water losses is heavily influenced by the maximum pressure. From this point of view, low pressure networks in towns, is a measure beneficial to minimize the loss of water pressure in the network with minimum value.
Water leak detection can be done by: passive control (determination of water losses by viewing production consequences), active control (systematic monitoring of the network) and regular audit. Departments that have acted to control water losses, have regard to: maintaining a quasi-constant pressure in the system, close to the technological needs (the pressure at the branch), upgrading and replacement of damaged pipes, ensuring the quality of execution in parallel with Periodic cleaning of the sections of the network, setting a limit to economic losses can be reasonably low (cca.20%), active control of technological parameters of the water network operation, including the loss of water, computerized system (SCADA, GIS) . Water quality in the distribution networks is determined by: the influence of the network constituent materials (iron, steel, concrete, cement, PE-ID, PVC, ceramics), residence / stagnation in the network, forming deposits, accidental contamination (through interventions network and the reservoir, or when pressure drops below atmospheric pressure in the network), poor quality of treated water, training and developing a video / biological treatment system by advanced methods captured biological stability (water Biostable).
Water losses in the distribution networks can be regarded as beneficial for combating biological processes , then fall stagnation / residential water pipes, lasts more than 7 days, and residual chlorine becomes imperceptible. Flow of water losses through leaks joints, holes and cracks in pipes / fittings can ensure minimum flow rates to combat biological film on surfaces inside pipes carrying water for human consumption. Reducing water losses became in the last 10 years the principal concern of all drinking water suppliers in our country.
Univ. Dr. Eng Ion MIREL
Polytechnic University of Timisoara
Department of Water Technology