Life of filter element

• The rate of decline in filter element performance in use is acceptable in terms of:
• User experience (flow rate reduction).
• Perceived cost (replacement frequency).
• User experience (maintenance frequency).
• Microbiological performance (if diminished through use).

Key indicators

• Regular maintenance continues until the filter element no longer reaches ≥25% of best flow rate (i.e., rate of recovery).
• If the device provides safe storage (a tap and/or limited access to dipping into the clean container), we recommend against stopping the flow at the end of filter element life.

Notes and exceptions

• Consumer perception may be that the life of a filter element continues until it is clogged beyond recovery.
• Dimensions requiring further research and clarification:
• User tolerance for decreased filtering efficiency (flow rate) over the design life of the filter element.
• Average flow rate recovery from regular maintenance.
• Consequences (in terms of LRV effectiveness) of using a filter element beyond its design life.
• Flow rate decreases increase the effectiveness of disinfectants due to increased residence times. Determine trade-off between higher disinfectant media costs per liter for increased flow rates and lower costs for reduced flow.

Supporting evidence

• Reference Design Beta Test Results. PATH, unpublished data, 2010.
• Roberts L, Chartier Y, Chartier O, et al. Keeping clean water clean in a Malawi refugee camp: a randomized intervention trial. Bulletin of the World Health Organization. 2001;79(4):280–287.
• Full list of supporting evidence and additional materials.