In my house we have a water butt connected to the gutter from the roof that fills when it rains. Could we use it as a keli mikvah if we connected two of them by a hose pipe so that the total water exceeded 40 seah?

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    – Isaac Moses
    Commented Jun 22, 2011 at 18:42

1 Answer 1


It depends on if the receptacle was originally made specifically to be attached to the ground or another structure that was attached to the ground (Shulchan Aruch Y.D 201:48; Pischei Teshuvah 33).

An interesting book is "The Secret of the Jew" by Rabbi Dovid Miller (A 2nd volume here.) Chapter 19 describes how to build a mikvah with various plans and costs. R' Miller learned in Slobodka, then moved to Oakland to become a banker. He focused on getting women to use a mikvah in the 30's when conditions were not as sanitary (and before antibiotics).

Edit: I found a case similar to yours in "The Secret", page 336. Howver, he requires both original intent to connect and a hole in the bottom (the tank is being used to regulate supply, not collect it). I don't know his source. To me it looks like either or would do, based on Shulchan Aruch above, and 204:7.

  • And Rabbi Yaakov Kamenetsky famously commented that you need to know Hebrew grammar. There was a place that Rabbi Miller miscalculated the required volume of a mikva because he confused "arba amot" with "arba'ah tefachim" (which would be like measuring in yards instead of feet).
    – Shalom
    Commented Jun 23, 2011 at 0:16
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    I'm not aware of an arba amos, just shalosh. The story that I heard in R' Yaakov's name is that while he was basing an amah on 6 tefachim, a tefach on 4 etzbaos and an etzba on a 'gudal, he based the 'gudal on his middle finger because the Rambam defines a 'gudal as an etzba beinuni. Because of a mistake in dikduk (etzba is female so should be beinunis- etzba beinuni means the 'gudal of an average man), one can be machshil a community in issur kares!
    – YDK
    Commented Jun 23, 2011 at 0:45
  • In any case, R' Miller requires 24 cubic feet+ (pg. 400 in my copy). According to a conversion calculator, that is about 680 liters. I don't know all the shittos, but that sounds like it over-does it.
    – YDK
    Commented Jun 23, 2011 at 0:55
  • @YDK, likely you're correct, I was hearing this all second-hand.
    – Shalom
    Commented Jun 23, 2011 at 13:07
  • @YDK, that's interesting. I also saw this book (years and years ago), and I thought I recalled him putting 40 se'ah = about 80 gallons.
    – Alex
    Commented Jun 24, 2011 at 6:17

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