Insights · Water
Non-revenue water - finding the water your scheme never bills
How small Kenyan water schemes measure the gap between network input and billed consumption, investigate its causes and assess the benefit of reducing it.
Joseph Gitonga · 3 min read
On this page 6 sections
Non-revenue water (NRW) is the difference between the volume entering a water network and the volume billed to customers over the same period. Measure those volumes first, then investigate where the difference comes from.
For a small Kenyan water scheme, this is both an operations and a billing task. Leaks need physical repairs; missing bills and inaccurate meters need a different response. A single loss percentage cannot tell you which action will pay off.
What counts as non-revenue water
The water balance distinguishes three components:
| Component | Examples |
|---|---|
| Real losses | Leaking mains, burst pipes and overflowing storage |
| Apparent losses | Under-registering meters, unauthorized use and consumption recording errors |
| Unbilled authorized consumption | Authorized flushing, firefighting or other use that is not billed |
A bill that has been issued but remains unpaid is a collections problem, not additional NRW volume. Don't count it in both categories. WASREB's NRW management guidelines explain the water-balance approach and the difference between its components.
Measure the same network over the same period
Record water entering the network from each borehole, intake or bulk purchase point. Account for exports where applicable. Record the reporting dates and use a consistent boundary.
Compare that input with billed consumption covering the corresponding period. Mismatched dates, incomplete billing and changes in tank storage can distort a monthly result. Label a result provisional if some meters have not been read or some bills are still outstanding for that reporting period.
Use zone meters where available. Without a measured inlet to a zone, you cannot reliably assign a share of the scheme's input to it. If input must temporarily be estimated, document the method and uncertainty and prioritize installing or checking a bulk meter.
Calculate volume before attaching a value
- Net system input is the water entering the network within the chosen boundary.
- Billed authorized consumption is the volume billed for the matching period.
- NRW volume = net system input minus billed authorized consumption.
- NRW percentage = NRW volume divided by net system input, multiplied by 100.
Illustrative example. Jay's scheme records 12,000 m³ of input and 7,800 m³ billed for the same period. The difference is 4,200 m³, or 35%. These are example figures, not measurements from a BillGrid customer.
Reducing NRW by one-third of that volume would recover 1,400 m³ and, with input held constant, reduce the percentage to about 23.3%. That is a volume improvement, not a guaranteed cash return.
Value each action on its own
- Correcting underbilling can increase billed revenue, subject to the tariff and collection of the resulting bills.
- Repairing a leak may reduce pumping and treatment costs. The saving depends on the costs actually avoided.
- Recovered water can support additional sales only where there is demand and capacity to deliver it.
- Authorized unbilled use may remain necessary; record it rather than treating all of it as recoverable sales.
Do not multiply every lost cubic metre by the retail tariff and call the result money recovered. Include repair, metering and investigation costs when comparing options. Setting water tariffs is a separate exercise from valuing a loss-reduction project.
Investigate billing gaps and physical losses
Start with checks that your team can verify:
- Connections missing from the account list or the month's billing.
- Persistent zero readings that need a site visit.
- Meter serials, age, condition and accuracy.
- Readings entered in the wrong units or against the wrong connection.
- Known bursts, overflowing tanks and repair delays.
A zero reading alone does not prove a bypass. A high night flow alone does not prove leakage; legitimate night use, intermittent supply and storage filling can also affect it. Ask the technical team to investigate before assigning a cause.
Compare zones carefully
| Zone | Input (m³) | Billed (m³) | NRW |
|---|---|---|---|
| Riverside | 3,100 | 2,630 | 15.2% |
| Market | 2,900 | 2,150 | 25.9% |
| Hillside | 4,000 | 2,020 | 49.5% |
| Estate B | 2,000 | 1,000 | 50.0% |
These add up to the example scheme's 12,000 m³ input and 7,800 m³ billed. Compare periods with the same boundaries and measurement methods before deciding an area has improved or worsened.
Make the review a monthly habit
In BillGrid, the water balance report brings recorded supply volumes and billed consumption together. Its usefulness still depends on complete, correctly dated inputs and bills. Review missing data before sharing a final committee report.
Record the finding, the proposed action, its cost and the next measurement date. Track water recovered separately from additional cash collected. For the billing steps behind the report, read a month of water billing or explore water billing.