Indicator systems are costly, both directly (i.e. the cost of development and implementation) and indirectly (i.e. opportunity costs and the potential for inadvertent generation of unintended consequences). It is difficult to capture complexity with water data and indicators, which can lead to developing too many indicators rather than concentrating on a core group. Besides, it is tempting on the part of central government to substitute ex ante control of water services with performance indicators. This can lead to retaining control of how sub-national authorities implement water policy, as they will probably make choices and decisions that allow them to perform well within the parameters of the indicator system, at the expense of other elements.