Evapotranspiration absorption beds

Evapotranspiration absorption beds

Evaporation absorption bed

An evapotranspiration absorption bed.


Cross section of an ETA bed (unlined) (after Patterson, 2006).

Evapotranspiration is the process that removes water from land covered by vegetation through evaporation (loss of water from soil or wet vegetation) and transpiration (loss of water from small openings in the leaves of plants and grasses).

Evapotranspiration absorption (ETA) beds reduce reliance on effluent absorption into the soil by maximising water loss through evaporation and transpiration.

Effluent is distributed through the bed by a system of slotted pipes. Capillary action draws effluent up from a lower gravel bed through sand to supply the root zone of vegetation (usually grass) on top of the bed, to optimise evapotranspiration.

Septic tanks are the most common treatment system used with ETA beds, but they may also be combined with composting toilets, biological filters, and aerated wastewater treatment systems (standard or with membrane filtration).

Common problems with ETA beds are:

  • bed vegetation cover not well maintained to maximise evapotranspiration
  • inadequate exposure to wind, or shading by trees, lowering the rate of evapotranspiration
  • uneven distribution of effluent caused by gravity feeding instead of by a pump or pressure dosing
  • beds too small for amount of effluent (hydraulic load).


Thursday 20 June
1,353,979 ML
2,581,850 ML
9,240 ML
1,320 ML
-7,624 ML
Thursday 20 June