The mechanism used is the structure of feed-in tariffs specified in the German Renewable Energy Law: when hydropower facilities comply with certain criteria (such as ensuring biological continuity of the river, or being built in a location where there are barrages or weirs), they are paid a higher-feed in tariff from electricity distributors, which is reflected in the energy bill paid by the end users. The additional remuneration is paid to hydropower producers for 20 years and varies according to facility size and output -smaller plants are paid higher remunerations per kWh than bigger plants to ensure their profitability, plants producing more than 5 MW are only paid for the increased part of production after modernisation. These are illustrated by voluntary agreements between water supply utilities and farmers to reduce pollution and water treatment costs (see OECD, 2012b). In the EU and the United States, farmers are paid for a variety of environmental stewardship measures, including reducing nitrate contamination.