The Total Non-Revenue Water of DMA’s is basically computed by getting the difference between the System Input Volume measured, and the Total Billed Volume delivered.
Non-Revenue Water = System Input Volume – Revenue Water

For Manila Water Company, The Total Non-Revenue Water is equal to the Total Water Losses since all the authorized consumptions are billed and metered.
Total Non-Revenue Water is further categorized into two distinct types: Real Losses, which is the physical loss within the system which is primarily, composed of background losses and leakages; and Apparent Losses, which is the loss due to metering inaccuracies, systematic data handling errors, and unauthorized usage. Total Non-Revenue Water can be composed of Real Losses, Apparent Losses, or a combination of both."