How to Lower Water Turbidity with a Roughing Filter

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Short Description

  • Problem: High water turbidity
  • Idea: A gravel filter
  • Difficulty: Easy but the water still needs to be desinfected!
  • Price Range: Cheap
  • Material Needeed: A container, gravel of different diameters
  • Geographic Area: Global
  • Competencies: Simple plumber skills
  • How Many people?
  • How Long does it take?


Roughing filters are used to separate solid matter from the water. They significantly improve the efficiency of sedimentation tanks. Because the fine solide particle in suspention in the water are so light, most of them won't settle in a normal sedimentation tank. The same sedimentation tank can be improved by filling it with gravel, rough filter material, of approx. 20-4 mm diameter. The fine solid particles flowing through the filter will touch a surface where they can settle as soon as they enter the tank.

Roughing filters usually consist of differently sized filter material decreasing successively in size in the direction of flow. The bulk of the solids is separated by the coarse filter medium located next to the filter inlet. The subsequent medium and fine filter media further reduce the suspended solids concentration. Roughing filters are operated at small hydraulic loads - filtration velocity is usually in the order of 0.3-1.5 m/h. Design and application of roughing filters vary considerably.


The water still needs to be desinfected! This can be with a Slow Sand Filter, a Solar Distiller, Sodis Bottles, water desinfection tablets or simply by boilling the water.

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[1] Wegelin, M., Boller, M., Schertenleib, R. (1987). Particle removal by horizontal-flow roughing filtration. J. Water Supply Research and Technology - Aqua, 36, 80-90.

[2] Wegelin, M., Schertenleib, R., Boller, M. (1991). The decade of roughing filters - Development of a rural water treatment process for developing countries. J. Water Supply Research and Technology - Aqua, 40, 304-316.

[3] CINARA. (Diciembre 1991). Proyecto integrado de investigación y demostración de métodos de pretratamiento para sistemas de abstecimiento de agua, Informe Resumen.

[4] Wegelin, M. (1986). Horizontal-Flow Roughing Filtration - A Design, Construction and Operation Manual. IRCWD Report No. 06/86.

[5] Wegelin, M. (1996). Surface Water Treatment by Roughing Filters - A Design, Construction and Operation Manual. SANDEC Report No. 02/96.

[6] Wegelin, M. (1997). Traitement d'Eau de Surface par des Préfiltres ˆ Gravier Un manuel de Conception, de Construction et d'Exploitation. SANDEC Rapport No. 03/97.

[7] Wegelin, M., Galvis, G., Latorre, J. (1998). La Filtración Gruesa en el Tratamiento de Agua de Fuentes Superficiales. SANDEC Report No. 04/98.

Note: The new roughing filter manual [5, 6 and 7] is on sale at Intermediate Technology Publications (it), 103-105 Southampton Row, London WC1B 4HH, England; Fax: +44-171-436 2013; E-mail:

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