The costs for maintenance of wastewater treatment plants usually amount up to 15–25 % of the total operation costs. Thus, the organization and strategy of maintenance activities play an important role for the agency.

Maintenance costs include the following: repairs on mechanical, electrical, electronic and civil parts and minor or major replacements like small or large parts for pumps, blowers or motors. They include internal personnel costs, material expenses and external services. Quantities of spare parts kept in stock and purchasing deals also influence the total maintenance costs.

For a first calculation maintenance costs can be derived from the investment costs as follows:

The above given cost assumptions are very roughly and have to be specified for each particular project. They depend mainly on the chosen maintenance strategy of the agency.

Maintenance is an important activity that should be performed in any type of facility, thus it is necessary for proper functioning and prevents damages whose repairing can be very expensive. Even low-tech options demand maintenance activities. Maintenance should be considered in a regular time basis (semestral, annual) into the costing and budget of the project.

Wastewater systems often suffer from a history of inadequate investment in maintenance and repair often due to large part of “out-of-sight, out-of-mind� nature which poses an inherent problem. This stands for both sewer systems as well as treatment facilities. The lack of proper maintenance results in the deterioration of the installed equipment and the construction itself.

The purpose of maintenance programs is to maintain design functionality (capacity and integrity) and / or to restore the system components to the original condition and thus functionality. The ability to effectively operate and maintain a wastewater treatment system depends mainly on site conditions, proper design (including selection of appropriate materials and equipment), construction and inspection, testing and acceptance, and system start-up.

Operation staff should already be involved at the beginning of each project, including planning, design, construction, acceptance and start-up. When the system is designed with future maintenance considerations in mind, the result is a more effective program in terms of maintenance costs and performance.