Another way of thinking about ...

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Another way of thinking about NRW is that it is the sum of physical losses and commercial losses. Also NRW is normally expressed as a percentage, so NRW = (Distribution input - billed volume) x 100 / distribution input

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The International Water Association (IWA) strongly advises against the use of NRW as a percentage for target setting. It is still frequently used as a percentage in reporting - especially to non-engineers. It should be understood that the % of NRW is dramatically affected by the annual volume of consumption and so is unreliable for target setting.

 

There are many references for this, here are some.

Who says %s by volume are unreliable?:

UK ‘Report 26’, 1980

German DVGW, Note Paper W391, 1986

UK ‘Managing Leakage’, 1994

American WWA Leak Detection & Water Accountability Committee, 1997

OFWAT, UK Economic Regulator, 1997

South African Bureau of Standards, 1999

Malta Water Services Corporation, 1999

New Zealand Water & Waste Association 2001

Water Services Association of Australia 2003

German DVGW, Note Paper 392, 2003

World Bank Institute 2005

Austrian OVGW 2009

 

I hope this helps.

Stuart

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