Operation and minor maintenance expenditure (OpEx) is expenditure on labour, fuel, chemicals, materials, regular purchases of any bulk water. Most cost estimates assume OpEx runs at between 5% and 20% of capital investments. Minor maintenance is routine maintenance needed to keep systems running at peak performance, but does not include major repairs.OpEx is normally borne by the service providers (or households, in the case of domestic facilities). [Source: Fonseca, C. et al., 2010. Life-cycle costs approach : glossary and cost components. (WASHCost briefing note ; no. 1). The Hague, the Netherlands: IRC. P. 4].