I have just finished building a grey water biological filter and would love to hear the different ideas and concepts others might have. I know there are other concepts that can be added such as a gravel/sand filter. But in my design, I did not want to increase the costs and preferred to let the Banana/plantains do the necessary work.

Factors to take into considerations

  • Tropical country (6 months rain / 6 months dry)
  • Appropriate technology = low tech
  • Gravity fed
  • Rural area
  • Grey water from the kitchen

My Setup

The grey water is coming from the kitchen. The kitchen is aware to limit the amounts of solids and grease/fats to throw in the kitchen sink. The grey water pvc pipe flows downwards to the first 3 plastic tanks (right to left) that act as grease traps. See picture below:

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In the first grease trap the oils/grease float to the top and then flows to tank #2 and #3. You can see that there is less and less oil/grease. First tank at the bottom of the picture is where the kitchen grey water enters. The 3 tanks at the top of the picture are the 3 plastic tanks that fill up with water that contains almost no grease/oils. This water will flow to the banana plants. The grease traps function in order to prevent the grease and oils to clog the soil. Note: The grease in the grease traps are removed on a daily basis. See picture below.

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The 3 nutrient filled water tanks without grease look clean a significantly cleaner than the 3 grease traps. These 3 water tanks also equalise and fill up at the same time. At the bottom of the middle blue coloured tank is where the water flows to the banana plants as soon as I open a pvc valve. As a way to prevent overflow in these 3 tanks I have added on top an overflow that runs to some ornamental tubers.

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When the tanks are full we open the valves that we need. See picture below:

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This water flows through perforated 1/2 inch pvc pipes to water the banana/plantain trees.

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Note: the banana plants have just been planted but this is not shown on the current pictures. I'll update those with time and growth.

Any conceptual and practical ideas or errors that may be suggested?

  • You might consider incorporating worms into your design also. Have a look at this example
    – daamsie
    Dec 20, 2014 at 12:38
  • 1
    14 months later - any updates on how this has worked in practice?
    – Ecnerwal
    Dec 20, 2014 at 18:55

1 Answer 1


In no order of importance:

  • are small insects or animals going to find inside the pipes to be a nice place to nest or otherwise obstruct?
  • are larger animals or people going to step on/trip/break the pipes?
  • if it is dry for six months of the year wouldn't it be better to store even larger quantities of water? Yet this requires some kind of treatment or the greywater will go off. And conversely, in the wet season will the system be adding even more water into the planting beds than is required?
  • larger scale projects usually have an organic component like a reed bed which does a great job of removing traces of grease and contaminants

This site raises some pertinent issues

  • if you don't use greywater within 24 hours then it can become unusable as bacteria multiply very rapidly in it
  • don't apply untreated greywater onto plants which have fruit or vegetables that are eaten raw. This is a precautionary health and food safety issue.
  • don't apply greywater onto saturated soils as it will runoff. What happens during the rainy season?
  • 1
    Good points. At the end of the perforated pipes I have caps that can be removed so that I can flush it out with water and pressure when obstructed. Animals/people will not walk on it since it is fenced off. People can also see it as an educational factor. Using too much water in the rain season could be an issue and time will tell. I'll update with time. The grey water is used on average every 4 hours. Banana "trees" link love grey water and eating these bananas are fine-No direct contamination. Oct 25, 2013 at 13:41

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