The gradual change in the climate, the substantial decrease in annual rainfall as well as the continuous increase of water demand, have as a result the need for water conservation and leakage management, to be a continuous activity and a integral part of the operation of a water utility.
Non revenue water (NRW) is water that has been produced and is “lost” before it reaches the customer. Losses can be divided into 2 main categories real losses such as leaks, and apparent losses such as inaccuracies of the water meters, theft, illegal connections etc.
|System Input Volume||Authorized Consumption||Billed Authorized Consumption||Billed Metered Use||Revenue Water|
|Billed un-metered Use|
|Unbilled Authorized Consumption||Unbilled Metered Use||
|Unbilled Un-metered Use|
|Water Losses||Apparent Losses||Unauthorized Use|
|Real Losses||Leaks on Transmission and/or Distribution Mains|
|Leaks on Service Connections up to Customer Meter|
|Storage Tank Leaks & Overflows|
The International Water Association (IWA) through the Water Loss Task Force has developed the Water Balance table which clearly presents the distribution of water among authorized consumption and water losses.
High levels of NRW are detrimental to the financial viability of water utilities, as well to the quality of water itself. That is why immediate actions have to take place by a water utility for the water loss control with the adoption of appropriate methodologies and international techniques. However for the project to be successful, the utility has to adopt these techniques as a part of long term strategy and at the same time to present constant dedication and commitment.
There is a practical process in order to break the problem of NRW into smaller categories and then proceed with the necessary actions.
First of all an assessment must be made and a calculation of how much water is lost. The IWA WLTF Water Balance Table can be used in order to calculate the NRW. The second question that should be asked is where is water is lost. Is it lost throughout the whole network or is it lost in specific sectors?
Why is it lost? What are the local circumstances in the network? Is the water lost through leaking, unauthorized use or apparent losses?
There are strategies that can be followed as long as the problem is identified correctly. Gather all the data you have, measure the results and compare them to the Real Losses management performance using the infrastructure Leakage Index, Identify and then prioritize the most effective actions.
Apparent losses equal to the loss revenue for the water utility and they are made up from the following:
- Water Theft that can be coming from:
- Theft from fire hydrants
- Meter bypasses
- Illegally tapping into water mains and water services
- Tampering with meters
- Revenue meter under-registration
- Meter reading errors
- Accounting errors
Keep in mind that the cumulative effect of above errors can be significant for the water utility. Reduction of apparent losses by reducing the theft results as well as reducing data errors results has a direct result of more revenue for the authority. An accurate metering result is essential as it is necessary to determine the true level of real losses as well as the increase of revenue. The more data the utility has the easier is to do get better decisions and design a far more efficient strategy.
The difference between water produced and water consumed (including Authorized Un-metered Consumption and Apparent Losses) is the volume of water physically lost. Referred to as ‘Real Losses’. Subtracting the Background Losses (Unavoidable Real Losses) from the total Real Losses reveals the potentially recoverable Real Losses.
Real losses are direct result of the following:
- The ageing of pipes or the damage that is been done to them.
- Pressure (excess, fluctuation or transients)
- Improper installation/materials
- Lack of or poor maintenance
- Seasonal weather variations
- Traffic loading and vibration
- Intermittent water supply
So, where does the water goes? Some of it will be Background Losses (smaller-than-pinhead size leaks throughout the system and uneconomical to fix). The rest is lost in reservoir overflows, water-main and water-service leaks and bursts.
Real losses are reduced by Pressure Management, leak detection, district metering and practical Asset Management. As a result of practicing the aforementioned steps is the reduction of real losses. All the steps that need to be taken into consideration are described in the opposite column.
Reduction of real losses has a direct impact on the operation of the utility as it decrease the operating cost thus defers the construction of new capital works. As an environmental result it saves water which is essential in a water scarce environment. Knowing where water is lost is the first step in reducing losses and promotes environmentally responsible water management.