Note that the unit metres/hour can be confusing, and is in fact a compaction of m3/m2/hour; that is, how much water volume can go through a certain area in one hour. Also sometimes this unit is expressed per day rather than per hour. For a fuller explanation of the relationship of water traveling through sand, check out Darcy’s Law explained.
Ref 01: Schulz, C.R.; Okun, D.A. (1984). Surface water Treatment for Communities in Developing Countries. IT, London. p.193. Available from www.developmentbookshop.com
Ref 02: Unpublished information supplied by WEDC, 1999.
Ref 03: Huisman, L; Wood, W.E. (1974). Slow Sand Filtration. WHO, Geneva, Switzerland. p.44. Available from WHO