“Question: If there is not adequate rainwater for a mikva to be filled up naturally is there any other way of filling a mikva?
Introduction:
A mikva needs to contain the volume of 40 se’ah (see Shulchan Aruch Yoreh De’ah Siman 201 se’if 1). The Gemoro explains in various places (Eruvin 4b; Pesachim 109a) that the reason for this measurement, which is derived from the pesukim, is because the Torah instructs that tevila be in an amount of water that contains the volume that could cover the body of an [average] person. The Gemoro explains that this volume is equal to three cubic amos, which equals 40 se’ah.
The general practice regarding forty se’ah is to consider forty se’ah as 1000 liters, which is the volume that satisfies virtually all opinions (The Shulchan Aruch ibid rules that 40 se’ah equals the volume of 44,118.5 cubic “fingers”. Some Poskim maintain that we calculate a finger as 2cm; some maintain that the correct measurement is 2.7cm. These differences are most significant in calculating the volume of 40 se’ah.) Therefore, although there are more lenient views regarding the calculation of forty se’ah, it is ideal that the mikva contains 1000 liters.
Discussion: If there is not enough rainfall to provide the entire 40 se’ah, it is possible to collect slightly more than 20 se’ah of rainwater, and then the remaining 19+ se’ah of water needed for the mikva can be added using tap water, utilising the mechanism of hamshocho:
Hamshocho is the name given to the passage of invalid she’uvim water over an area that renders the invalid she’uvim water kosher for tevila (see Shulchan Aruch Siman 201 se’if 44 that writes if the [invalid she’uvim] water flowed outside of the mikva [e.g. on the ground adjacent to the mikva] and only subsequently flowed into the mikva they do not invalidate the mikva as long as this [hamshocho] water is the minority of the initial 40 se’ah).
Hamshocho must occur over ground or, according to the Shulchan Aruch, over an item that does not invalidate the mikva (see Shulchan Aruch ibid that clearly writes that hamshocho is valid whether it occurs over ground or whether it occurs over any item that does not invalidate the mikva [water]).
Hamshocho under certain and specific conditions can eliminate the invalidation of she’uvim from the water:
• Hamshocho needs to occur over a distance of three tefochim (Shulchan Aruch ibid se’if 45).
I.e. between the tap or container from which the she’uvim is poured and the mikva the water must travel a distance of three tefochim for hamshocho to be effective.
• As mentioned previously, according to the Shulchan Aruch hamshocho is also valid if the water flows over an item that never had the Halachic status of a kli (Shulchan Aruch ibid se’if 44 & 46).
• The Remo (ibid se’if 46) quotes an opinion that maintains that hamshocho is only valid if the water flowed over absorbent ground. The conclusion of the Remo himself is that one should ideally be stringent and follow this opinion.
Conclusion: Returning to our question, if it is possible to collect 20+ se’ah of rainwater in the bor, the remaining 19+ se’ah of water can be added using regular tap water (which is assumed to be she’uvim) with hamshocho; and hamshocho will eliminate the invalidation of she’uvim and the mikva will now be kosher for use.
Once the first 40 se’ah has gathered (the first 20+ se’ah must be rainwater and the subsequent 19+ se’ah can be regular she’uvim with hamshocho), then any amount of regular tap water can be added (even without hamshocho), and the mikva remains valid.
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