Pre-filter design

  • Devices incorporate a pre-filter that can be cleaned by the user and that helps to reduce clogging of primary filter components and does not impede filling the device.

Key indicators

  • Pre-filter is reusable and can be washed by hand.
  • Pre-filter flow rate does not restrict filling of the actual treatment device.

Notes and exceptions

  • Pre-filter performance and required cleaning frequency will depend on water quality at the point of use.
  • Pre-filters that visibly stain or collect debris can be a desirable indicator of water quality improvement for the end user (“If my pre-filter is dirty, it must be removing bad things from my drinking water.”). Where the source water is not turbid, the pre-filter staining may be the only indicator of water quality improvement outside of taste and/or smell.

Supporting evidence

  • Clasen T, Naranjo J, Frauchiger D, et al. Laboratory assessment of a gravity-fed ultrafiltration water treatment device designed for use in low-income settings. American Journal of Tropical Medicine and Hygiene. 2009;80(5):819–823.
  • Full list of supporting evidence and additional materials.

Woman kneeling in an outdoor courtyard, washing the pre-filter of an HWTS device.

Pre-filters should be cleanable by the user. Photo: PATH.