Can I use a pool for daily tevilah or a mikvah with an active filter?

For the purposes of a men’s mikvah, although there’s merit in using a kosher mikvah of rainwater, 40 se’ah of regular she’uvin (“drawn”) water is sufficient, provided it’s in the ground and not in a utensil.¹ A swimming pool built into the ground usually qualifies in this regard.

Most poskim require the water of a men’s mikvah to be stationary and not flowing (zochalin), though a minority allow leniency for a men’s mikvah in times of need.² If water is flowing out — e.g., through a leak in the wall — it generally has the halachic status of zochalin (see issue 812).

What about an active pool-style filter? The flow of the filter doesn’t leak automatically like a crack. Moreover, the pump could perhaps be compared to a person manually drawing water from the mikvah with a bucket, which certainly doesn’t render the mikvah to be zochalin. On the other hand, the filter is continuously “leaking,” and all the water of the mikvah is moving toward leaving.³

Halacha states that if water overflows during immersion and then slides back into the mikvah, it’s not a concern of zochalin (see issue 813). Reb Moshe Feinstein argues that the same should apply to a filter, which sends the water back into the mikvah after filtration.⁴ However, there are differences: (a) the filter removes a lot of water, unlike a minor overflow; (b) the water pumped out doesn’t return “on its own;” (c) some consider water spilling into the mikvah also as zochalin.⁵

Another possible leniency may apply if the water is being pumped at a higher level, below which at least 40 se’ah remain stationary,⁶ though there is much halachic discussion on this scenario (see issue 813).

In practice, even in a men’s mikvah, the filter should be turned off before tevilah. But if that’s not possible, there is still merit in tevilah with a running filter for men, based on some of the above considerations.

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