Drainage Boards are autonomous public bodies under the direct control of the board members. The number of members is set out in the constitution of the board and these vary depending upon the size of the drainage district. The constitution of a drainage board has to be agreed with the Minister of the government department at the time it is set up. The members referred to, are those elected every one or three years by the agricultural ratepayers. (The frequency of election is dictated by the Act of Parliament under which the board was constituted.)

In addition to the elected members, there are appointed members who are nominated to the board by local authorities. These members are there to represent the interests of residential, commercial and industrial property within the District.

The proportion of elected and appointed members is based upon the relative contribution from agricultural and non-agricultural land. It is pro rata where the agricultural ratepayers pay the majority of the income, but where non-agricultural ratepayers provide the majority of income, the appointed membership is limited to a majority of one.