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Three Mediterranean countries subject to Intermittent Water Supplies and two European countries with Continuous Water Supplies are collaborating in this project. The aim of the project has been to identify situations in water distribution systems in each country where bacterial regrowth can be demonstrated, to determine the extent of regrowth whether or not it constitutes a threat to public health, and ultimately to model the water distribution systems in terms of hydraulic, conservative and non- conservative chemical parameters, and bacteria (based on Heterotrophic Plate Counts), and use these models to examine various control scenarios to limit the extent of bacterial regrowth.

Water distribution systems in each country have been selected and the necessary information gathered to model the systems hydraulic, physical and chemical behaviour using the Epanet public domaine package published by EPA. The more sophisticated Performance Q event-driven model developed by our Portuguese partner has been interfaced with Epanet, and Performance Q has been expanded to enable growth, death and detachment to be modelled. The whole has been encapsulated in an MS –Windows based easy to use shell. The Enhanced performance Q model is now in the final stages of testing.

The data collected by the partner organisations is clearly pointing to the situations which enhance bacterial growth, namely systems in which TOC > 5mg/l (usually surface water sources) with temperatures of 15^oC or above, systems with long retention times (long mains, service reservoirs, and household storage tanks in countries with intermittent water supplies), and low (<0.3mg/l) chlorine concentrations. Variable velocity due to fluctuating water demand also has the effect of detaching biofilm from pipe walls, causing sudden increases in suspended bacterial numbers.

When water pumping starts after a period of no flow in an intermittent supply, poor water quality has been shown to occur due to infiltration of contaminated water and/or detachment of biofilm from the pipes.

A clear potential health risk has been demonstrated in household water storage tanks, where bacterial increases of up to 5 orders of magnitude may occur in surface derived waters over a seven day period.

1. Monitoring distribution networks in each country for hydraulic, chemical and bacterial parameters.
2. Hydraulic calibration and validation of Epanet models for each network.
3. Determination of kinetic coefficients of growth and death of relevant bacteria, plus chlorine decay kinetics in bulk and wall effects.
4. Behaviour of bacteria in household storage tanks.
5. Biofilm measurement of growth and detachment from pipes.
6. Demonstration of infiltration in two intermittent water distribution systems.
7. Epidemiological study on populations using untreated water sources.
8. Formulation and evaluation of Enhanced Performance Q model.
9. Formulation and validation of plug flow model of bacterial growth and death.

• Evison, L. and Sunna,N. (2001) Microbial Regrowth in Household Storage Tanks. JAWWA Vol 93 (4)
• Hashwa, F. and Tokajian, S. (2000) Change of Water Quality in the Distribution System of a Residential Area in Beirut. Presented to IVth International Conference on Water Supply and Water Quality, Krakow, Poland, 11-13^th September 2000.
• Menaia, J., Alves, R., Mesquita, E., and Tarvares, J.T. (2000) Protein Contents as a Measure of the Active Biomass in Monitoring Drinking Water Pipe Biofilm Colonisation. Submitted for publication in Water Science and Technology.
• Tokajian, S., Sunna, N., Evison,L., and Hashwa, F. (2000) Microbial Regrowth in Household Tanks. Poster paper, 1^st World Congress of the International Water Association (IWA), Paris, 3-7^th July 2000.
• Vieira, P. and Coelho, S.T. (2000) Chlorine Decay in Water Distribution Systems.5^th Water Congress, Lisbon, Portugal, April 2000.