Reed beds can be built in a number of variants but mainly they are of the horizontal flow or down flow configuration. The two types can also be used in combination where necessary.

Horizontal flow reed beds can be of the surface flow or sub-surface flow type. By far the most common type is the sub-surface flow and is often used for final polishing or tertiary treatment applications. Surface flow reed beds are often used for metals removal and settlement applications.

Sub-surface horizontal flow reed beds consist, mainly, of an excavation approximately one metre deep which is made waterproof. The bulk of the excavation is filled with small, single sized media such as gravel with larger media at the inlet and outlet ends. A piped inlet distribution and drainage system is installed and reeds are planted directly into the gravel media. The effluent to be treated passes through the gravel media and the level of the effluent controlled by means of an adjustable, level control pipe in an external chamber.

Both the process and physical design of reed beds has changed significantly over the past few years to increase the cost-effectiveness of these systems. These developments have been due, principally, to development work by ARM Ltd.