Water distribution Professor Nick Gray Centre for the
Water distribution Professor Nick Gray Centre for the Environment Trinity College University of Dublin © Tigroney Press
Water distribution Learning objectives: • To understand the mechanisms and problems of transportation and delivery of treated water to consumers Fundamental questions that need to be tackled: Ø How do we get water to consumers? Ø How do we prevent contamination? Ø Who needs what in terms of supply?
Water distribution Water Services Cycle After treatment water enters the distribution system where it is carried via trunk mains to a service reservoirs which then feed the distribution network
Water distribution Distribution system showing zones loop and spur mains Water supply zones <50, 000 people
Water distribution Pipe materials used in distribution Older materials: • Iron - discolouration, elevated iron concentrations, iron particulate matter, sediment problems • Asbestos cement – release fibres into water. Concentrations of 2 x 106 L-1 common; USEPA MCL 7 x 106 fibres L-1 • Linings- Both materials commonly lined with coal tar or bitumen-release polycyclic aromatic hydrocarbons (PAHs). Nearly all PAHs are carcinogenic. EU DWD sum of four reference PAHs <0. 1 ug. L-1 while most hazardous PAH bezo(a)pyrene <0. 01 ug. L-1. Also found in soot vehicle emissions, burning hydrocarbon fuels. New materials: • u. PVC (unplasticised polyvinyl chloride) • MDPE (medium density polyethylene)
Water distribution Distribution Mains Trunk Mains: • Transporting large volumes • Source to treatment plant to service reservoir • No branch or service pipe connections Distribution Mains: • Varying sizes: 100 or 150 mm generally larger in cities - rigid; smaller sizes 90 or 63 mm are flexible • Highly branched • Used for connections ØLoop main (equalizes pressure, water rapidly used and mixed) ØSpurs (cul-de-sacs, lower pressure at end, water old, build up of animals debris, fibres etc).
Water distribution Pipe replacement
Water distribution
Water distribution Dublin water mains rehabilitation scheme 2015 Larger mains or upgrades needed to laid along road or tunnelled.
Water distribution Trunk mains failure (July, 2017) at Donore near Drogheda. Mains fed Staleen WTP leaving 70, 000 people plus businesses in Louth and Meath without water for 6 days. The iron main was 50 years old. There are 63, 000 km of water distribution pipe in network in Ireland 10% is in need of urgent repair.
Water distribution Water service reservoirs • Demand for water varies diurnally • Service reservoirs ensure peak demands met so smaller pumps and mains used for average daily flow rather than peak flow (50 -80% higher) • 24 -35 h retention/storage • Concrete or smaller units in brick or steel • Normal reservoir design or in flat areas towers are used
Water distribution Under Pressure § Pressure in main normally produced by hydraulic head, rarely by direct pumping § Water pressure can be measured as hydraulic head (m or ft) or pressure (bar or psi). § 1 bar raises water 10 m. § Minimum pressure in UK is 7 m or 0. 7 bar (OFWAT) § Normal pressure to house 10 m or 1 bar (Thames Water) § Mains pressure 2 -4 bar (30 -60 psi) § Minimum head required to fill attic storage tank and for fire fighting considered to be 10 m
Water distribution § >70 m head results in unacceptable loss of water via leaks, excessive wear on household equipment and excessive noise. § Flats and office blocks require own pumps to fill storage tank. § Fractured mains or hydrants can result in rapid loss of water. Main causes for low pressure: Ø Inadequate pumping facilities Ø Water mains that are too small Ø Reduced pressure from the water main as a result of leakage, equipment failures or blocked service pipes To convert pressure (bar) to head (m): p = 0. 0981 h SG Where h = head (m); p = pressure (bar); SG = 1. 0
Water distribution Under Pressure The amount of water released by a mains fracture can be substantial as is the case on 27 th September 2014 in Bristol. A fractured trunk main required stranded householders to be rescued by inflatables. 24, 000 households were without water for three days, leading to long queues at water tankers.
Water distribution Under Pressure § Mythe Water Treatment Plant, Tewkesbury § 22 nd July, 2007 Flooded by R. Severn § 160, 000 properties cut off – 350, 000 people Non-potable supplies restored: 50% by 31 st July, 98% by 1 August Water only became drinkable by 7 th August! Full report: http: //www. stwater. co. uk/upload/pdf/The_Final_Gloucester_2007_Report. pdf
Water distribution • Fire fighting and mains flushing Water Hydrants • Location depends on water company and fire brigade needs • Tested regularly by fire brigade Diameter of main • 100 mm spur • 75 mm loop Distance from plaque
Water distribution Hydrant parts: 1. Standpipe 2. Standpipe with check valve 3. key 4. Hose (5 m) 5. Female house coupling 6. Male hose coupling
Water distribution Service pipe Single dwelling 25 mm diameter (usually 13 mm) Several dwellings >25 mm Old materials: Mild steel, Iron, Copper, Lead, (all suffer corrosion)replacement programme New material: Polyethylene
Water distribution
Water distribution Boundary Stop Valve
Water distribution Water meters Either in own box or shared with boundary stop tap
Water distribution Service pipe replacement <1965 houses earthed via supply pipe Pipes colour coded: • Blue - water • Yellow - gas • Black/Red – electricity • Grey – telephone • Brown/concrete- sewerage
Water distribution Joint Supply Pipes Common on older local authority housing, older terraces etc. Problems: ØAccess –pass through cellars ØLow pressure at end house ØMaintenance and repair problems
Water distribution Leakage q Not all treated water gets to the consumer due to leakage from damaged and ageing pipe work. q Leakage can account for >40% of all supplied water in some areas q Average leakage rate in England Wales is 24% (i. e. 3608 ML d-1) 17% - distribution mains; 7% - supply pipes q While it is relatively easy to initially reduce leakage by 5 to 10% by employing dedicated leak detection and repair teams, once the major leaks have been dealt with then it becomes increasingly more expensive and time consuming to locate and repair the smaller leaks. q In practice it has not been practicable to reduce leakage in the UK below approximately 24% for the past ten years in spite of increasing investment in detection and repair each year. q Irish Water and leaks: https: //www. water. ie/projects-plans/national-projects/leakage-reductionprogramme/
Water distribution Water Leakage in England Wales 1992 -2005
Water distribution Quality problems due to distribution Normally associated with deterioration of network ØIron, asbestos, PAH ØBiolfilm, micro-organisms, regrowth of pathogens ØAnimals ØOdour and taste Quality problems due to household plumbing Normally associated with poor installation and maintenance of plumbing Ø Ø Ø Corrosion Lead, Copper, Zinc Micro-organisms Fibres, asbestos Odour and taste Lead reduction plan for Ireland: https: //www. water. ie/projects-plans/nationalprojects/lead-in-drinking-water/
Water distribution Conclusions v Distribution system designed to ensure continuity of supply v Pipe materials can lead to contamination v Biofilm and animals also cause problems v Unlike other utilities consumer responsible for maintenance of supply to house v Vast majority of quality problems arise due to household plumbing problems
Water distribution Further details For further information the following chapters gives a detail account of the various aspects of distribution and plumbing supply problems. Gray, N. F. (2008) Drinking water quality: problems and solutions, Cambridge University Press, Cambridge. Problems arising in the distribution system Ø 20. The distribution network Ø 21. Aesthetic quality Ø 22. Asbestos Ø 23. Coal tar linings and polycyclic aromatic hydrocarbons Ø 24. Animals on tap Ø 25. Pathogens Problems in household plumbing systems Ø 26. Household plumbing systems Ø 27. Corrosion and metal contamination from pipework Ø 28. Micro-organisms, fibres and taste
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