Q. What is the correct amount of water needed for tisha kavim?
A. Poskim quote different amounts for the nine kavim of water. They vary from approximately 11.3 liters to 17 liters, 18.5 liters or 22 liters (Nefesh Chaya, Beis Boruch on Chaye Adam 1; p. 412. and others).
On question 1945 we wrote: Horav Shlomo Miller Shlit’a pointed out that one kav is equal to the volume of 24 eggs and tisha kavim is then 216 eggs.
According to the measurements of Rav Chaim Noeh, one egg is equivalent to 57.6 cc, so nine kavim would equal to 12.44 liters (Shiurei Torah p. 263). Following the opinion of the Chazon Ish, it equals 21.6 liters (Midos Veshiurei Torah p. 300).
One has to measure his own shower’s water volume delivery and the time it takes to reach that required volume, as they all vary.
When taking a shower for this purpose, one should first stand under the shower spout and then open the water, so the water immediately goes over all of him as he opens the faucet.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit’a