Reference for constructing Martin Crawford’s gravity filtered reservoir

Greenish water in small reservoir
Small reservoir in Langdale Forest, by Oliver Dixon

Martin Crawford has information about creating a reservoir in Agroforestry News vol 23 no. 2, PDF available online (though pricey)

Key detail

  • Design derives from maximum size of plastic pond liner: 25m x 6m
  • Each reservoir 3.5m x 20m x 1m deep = 70 cubic metres
  • Use gravity fed where possible
  • Any water fed into pipes needs to be filtered
  • Circulation requires powerful pump, MC uses 4 x 180W solar panels to power Lorentz pump
  • Filter is an upwards-flow (much easier to clean) stone-gravel-grit system, using upcycled 1200 litre plastic water tank (previously used for transporting fruit juice):
    1. Bottom layer 30cm deep, 40mm stone
    2. Middle layer 30cm deep, 10mm gravel
    3. Top layer 30cm deep, 4mm grit

|        | → clean water out
|  grit  |
| gravel |
| stone  |
|________| ← reservoir water in