Sizing a reed bed for grey water

What would be an appropriate size reed bed to handle the following:

* Sink and dishwasher waste water from kitchen only.
* Hand washing once daily, dishwasher used once a week.
* Effluent from the bed would be used to water plantings along the house.
* Zone 7 environment, over story of oaks providing deep shade in summer. Water source is on the East side of house.

Appreciate your input.

John McGinnis

john mcginnis wrote:What would be an appropriate size reed bed to handle the following:

* Sink and dishwasher waste water from kitchen only.
* Hand washing once daily, dishwasher used once a week.
* Effluent from the bed would be used to water plantings along the house.
* Zone 7 environment, over story of oaks providing deep shade in summer. Water source is on the East side of house.

Hi John,

The Irish EPA Code of Practice on such things suggests that for a standard soil based constructed wetland for all septic tank effluent you'd need 20m2/person to do the same job as a standard electrical treatment system (termed secondary treatment) plus an additional 10m2/person for tertiary polishing if you need it extra clean. For a gravel reed bed I'd recommend about 8m2/person plus an additional 2-4m2/person for tertiary treatment (the code only requires 5 and 1m2 respectively, but in my experience that's too small).

For your house, with such low water usage you could estimate your total volume and then reduce the system size accordingly. The above figures are for 150 litres/p/d, so if you use one third of that amount, you could reasonably reduce your overall size by a factor of 3.

The shading by oaks may be a problem if it's too heavy. Trim them back so the sun can get at the bed.

As regards reusing the water; that should be ok even for food plants, as long as you use eco-friendly (essentially food grade really) detergents, cleaners, cosmetics etc in the house.