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.