NRW (Non Revenue Water) is water that has been produced and is “lost” before it reaches the customer. NRW monitoring is the process of monitoring losses in pipe distribution networks.
High levels of NRW are detrimental to the financial viability of water utilities, as well to the quality of water itself.
NRW is typically measured as the volume of water “lost” as a share of net water produced however, it is sometimes also expressed as the volume of water “lost” per km of water distribution network per day.
Potential Impacts of NRW
«Do water losses really have such a bad impact? Water losses are always with us…»
When it comes to operating water supply systems, NRW is a clear obstacle to sustainability, as the following list of potential impacts shows:
- Economic impacts: Costs for exploiting, treating and transporting water which is lost on its way to the customer without generating any revenue for the water utility. Pipe bursts and leaks necessitate expensive repair works and may also cause considerable damage to nearby infrastructure.
- Technical impacts: Leakage leads to reduced coverage of the existing water demand, possibly so much so that the system can no longer operate continuously. Intermittent supply will cause further technical problems by air intruding into the pipes and will tempt customers to install private storage tanks.
- Social impacts: Water losses result in customers being adversely affected by supply failures, such as low pressure, service interruptions and unequal supply. There are also health risks which may arise from the infiltration of sewage and other pollutants into pipe systems under low pressure or intermittent supply.
- Ecological impacts: Compensating water losses by further increasing water extraction places additional stress on water resources and requires additional energy and thus causes carbon dioxide emissions that could have been avoided.
How many loses can we have in water distribution networks?
In water distribution networks there are commercial loses and real loses.
Commercial losses, sometimes called «apparent losses», include water that is consumed but not paid for by the user. In most cases, water has passed through the meter but is not recorded accurately. In contrast to leaks or reservoir overflows, the lost water is not visible, which leads many water utilities to overlook commercial losses and concentrate instead on physical losses.
Commercial losses can amount to a higher volume of water than physical losses and often have a greater value, since reducing commercial losses increases revenue, whereas reducing physical losses reduce the production costs. For any profitable utility, the water tariff will be higher than the variable production cost — sometimes up to four times higher. Thus, even a small volume of commercial loss will have a large financial impact.
Commercial could be further broken to:
- Meter reading errors – caused by unexperienced or corrupt meter readers, human errors, condensation on meter dialers and others. The best solution for avoiding those is the application of smart water meter reading.
- Meter under-registration – Inaccurate meters tend to under-register water consumption leading to reduced sales and therefore reduced revenue. Meters seldom over-register consumption. Again the smart metering together with alarms for under consumption could be part of the solution. However that has to be combined at least with basics such as to be installed the correct water meter under the correct location.
- Water theft – again smart water meter reading could be part of the solution since it is able to notify about tamper evets, fire alarms for abnormal or no consumption and help in identifing potential bypasses and illegal connections.
- Water accounting errors – errors in billing and accounting could be avoided by an integration between smart water meter reading and billing.
Physical losses, sometimes called «real losses»or «leakage», includes the total volume of water losses minus the commercial losses. Leakages could be:
- Reported bursts – Visible and usually quickly reported by the public or observed by water utility staff. They have a short awareness time.
- Unreported bursts – commonly occur underground and are not visible at the surface. Water management personal usually discovers unreported bursts during leak detection surveys and often have a long awareness time.
- Background leakage – an accumulation of very small leaks that are difficult and not cost effective to detect and repair individually.
- Leakage & Overflows from the Utility’s Reservoirs and Storage Tanks – to prevent those observations can be done by installing a level monitoring data logger which will then record reservoir levels automatically at preset intervals.
All physical losses could be well detected and even prevented in timely manner by combined application of ThingsLog Smart Water Monitoring solutions for flow and pressure monitoring. However no technology can help if the the utility operator does not implement a continious NRW management process.
What is NRW management?
NRW Management consists of knowing what is happening with the water supplied and taking corrective action to reduce water that is wasted.
NRW Management offers the following benefits to water utilities:
- Sustains water supplies and increases protection of potable water supply (e.g. reduces risk of backflow which can cause contamination)
- Reduces energy and treatment chemical costs
- Reduces water treatment and pumping costs
- Lowers down wastewater treatment costs
- Defers capital expenditures
- Reduces damage to infrastructure
- Improves systems hydraulics and utility efficiency
- Reduces unauthorized usage
- Reduces potential claims due to water damage
- Improves public awareness of water’s value
- Improves environmental protection as water resources become scarcer.
The role of monitoring in NRW management
Without monitoring the utility operator would not know how to really to quantify NRW and would not know the impact of their actions in preventing non revenew losses.
Monitoring has also a preventive manintenance role by detecting pressure deviations.
Active NRW Management is more cost effective when using zones to measure the non revenew losses, where the system as a whole is divided into a series of smaller sub-systems for which NRW can be calculated individually.
These smaller sub-systems, often referred to as District Meter Areas (DMAs) should be hydraulically isolated so that you are able to calculate the volume of water lost within the DMA.
When a supply system is divided into smaller more manageable areas, the utility can better target NRW reduction activities, isolate water quality problems, and better manage overall system pressure to allow for 24/7 water supply throughout the network.
Here are a set of criteria to create a preliminary DMA design. They must be tested either in the field or using a network model:
- Size of DMA (e.g. number of connections—generally between 1,000 and 2,500);
- Number of valves that must be closed to isolate the DMA – should be kept to a minimum – natural boundaries should be used where ever possible;
- Number of flow meters to measure inflows and outflows (the fewer meters required, the lower the establishment costs and more accurate flow measurement );
- Ground-level variations and thus pressures within the DMA (the flatter the area the more stable the pressures and the easier to establish pressure controls);
- Easily visible topographic features that can serve as boundaries for the DMA, such as rivers, drainage channels, railroads, highways, etc.
Estimating losses in a DMA
To estimate the level of leakage in the DMA, the operator needs to calculate the system’s Net Night Flow (NNF), i.e. the portion of night flow directly attributed to leakage. The Net Night Flow (NNF) is determined by subtracting the Legitimate Night Flow (LNF) from the Minimum Night Flow (MNF). Monitoring systems such as ThingsLog flow monitoring solution could help in determining and monitoring the Night Flow.
The MNF is the lowest flow into the DMA over a 24-hour period, which generally occurs at night when most consumers are inactive. This MNF can be measured directly from the data logging device or the flow graph (example above). Although customer demand is minimal at night, water operators still have to account for the small amount of legitimate night flow, i.e. the night-time customer demand, such as toilet flushing, washing machines, etc.
Like all other leakage reduction methodologies, implementing district metered areas is not a quick fix, but requires long-term commitment on the part of a water utility’s management and operations staff.
Once NRW is reduced to an acceptable level, the staff should set up a monitoring regime for DMA inflows. In its simplest form, this consists of a monthly reading of the flow meter totaliser. The installation of a data logger to record flows will however reveal more detailed data, including the daily NNF, which enables more precise corrections to the system.
Leakage is proportional to the pressure in the system.
Similar to water flows into the DMA, the DMA average pressure will change over a 24-hour period. Pressure is directly proportional to flow due to frictional head losses within the system, and thus when the DMA has its lowest inflows, the pressure will be at its highest, see the 2nd figure on the right. This is because frictional head-loss is proportional to velocity, so when flows are low, the velocities in the pipes are also low and less head-loss occurs.
DMA flow monitoring could be combined with pressure management and monitoring for achieving better visibility and results.
Pressure management and monitoring
Pressure management comprises the adjustment and control of water pressure in water supply systems. It is an important component of NRW reduction, as reducing the water pressure in a pipe network can decrease leakage.
PMA (Pressure management areas) are typically combined with DMA.
Typically, a Pressure Regulating Valve (PRV) is installed on the Feeder to the DMA at its entry point. This PRV arrangement ensures equitable pressures within each DMA of an operational zone. PRV is typically combined with remote pressure and flow monitoring before and after the PRV.
ThingsLog pressure monitoring solution could feed up pressure readings to the Dynamic Pressure Management System (DPMS). DPMS is an arrangement of PMAs, which sets the PRV to adequate pressure setting during high demand hours and reduces the pressure within the DMA during low demand hours.
During the low demand hours (night hours) the pressure within the DMA shoots up, causing increased leakage through the existing breaks and ruptures on pipeline. As the PRV reduces the pressure, the resulting leakage is also reduced. This has emerged as a popular practice to control NRW at DMA Level and is quite successful.
How can ThingsLog help?
We offer a solution for combined DMA and PMA zone monitoring based on own low power data loggers, monitoring software and a mobile app.
Data loggers have IP68 protection level and are able to operate on locations with difficult access such as the manholes of the water utility operators.
ThingsLog data loggers are able to transmit data with cellular, NB-IoT or LoRa/LPWAN network connectivity.
Each logger can capture simultaneously readings from two pressure sensors and two flow meters.
Loggers support SCADA mode in case of an alarm or unusual event.
The utility gets ready to use package of loggers, monitoring software and a mobile app. Solution could be deployed in the cloud or as a private deployment on utility servers. If the utility chooses the first option ThingsLog offers also a model as a service which lowers significantly the initial investment costs of the utility for deploying DMA/PMA zones.
Finally the solution could be combined with ThingsLog remote meter reading which gives complete snapshot in any particular moment not only on the real loses but also on the commercial one.
NRW management and monitoring process is important for water utility operators. By sectorizing the distribution network to DMA and PMA NRW could be monitored, estimated and managed more easily. Monitoring of flow, pressure and level for DMA and PMA is important for the successfull implementation of NRW management process.
ThingsLog solution for smart water management and monitoring could help to utilities to implement DMA/PMA monitoring in smart and cost efficient way.