The IR-70E does fit in the IF-10A housing. We've sold a lot of these filters for this housing. The IR-70E reduces more contaminants than the IR-10A such as lead. Because of the additional contaminant reduction, the flow rate is slower through the filter. If you do not have the IF-10A hooked up to a separate drinking water faucet, you may want to consider the AquaPure AP117. This has a similar flow rate as the IR-10A.
http://www.waterfilters.net/Waterpik-IR-70E-Under-Sink-Water-Filter_p_97-379.html http://www.waterfilters.net/Aqua-Pure-AP117-Water-Filter_p_122-503.html
Thank you,
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