The main difference is a smaller number of countries where the use of flat fees and decreasing block tariff structures were detected. This relative inertia can be explained by the complexity attached to changing tariff structure. Moving from flat fees to volumetric rates, for instance, entails the installation of meters, and changing the structures of volumetric tariffs {e.g. changing the number or size of blocks in an increasing-block tariff [IBT] scheme) requires that impacts are assessed on the financial sustainability of the provider, the affordability for different consumer groups and short- and long-term impacts of demands. It also requires extensive consultation with the public. Even in countries where IBTs prevail, their design varies across providers in terms of the number and size of blocks. The diversity of tariff structures in a country is generally linked with the degree of decentralisation of the tariff-setting process.