This document, developed by the FAO, presents the conceptual and practical approaches proposed for auditing multiple services in large irrigation systems. It is called MASSMUS, which stands for Mapping System and Services for Multiple Uses of Water Services.

It is a step-by-step progressive process that starts with a rapid appraisal procedure (RAP), then proceeds with further steps related to capacity, water balance, cost and development of a vision, and the design of interventions to modernize the management set up and operation techniques. Some adaptation to the specific function and constraints, inputs and outputs for MUS has been made where necessary.

An important aspect of the MASSMUS approach for auditing water services to irrigation systems is the reference for benefits, which is associated to each type of service. Generally references for irrigated agriculture are clear and reliable: yields and water entering the command area (CA) and water used by crops during evapotranspiration are reasonably well known. The benefits of irrigation are often taken to be the monetary value of the total yield throughout the CA.