The Shulchan Aruch in Orach Chayim 88:1 states:
Baal Keri is permitted in Torah, reading the Shema, and prayer without immersion and without washing with nine Kabs of water,
Is bathing in 9 kav of water equal to immersing in the mikveh? If not, is it permissible bedieved? If yes, how many litres is 9 kav according to Chacham Ovadia Yosef?
It's a more complex story, and the short answer is clearly no. For example a convert or a woman after her period or a male who would want to enter the Temple Mount can't go and pour 9 kavin of water upon themselves instead of a mikveh. There were 10 decrees of Ezra (Bava Kama 82a), among them the last one requiring a baal keri (person having a seminal emission) to go to the mikveh before engaging in prayer. This requirement is discussed at length from Berakhot 21b, and the conclusion is that in certain cases it is not necessary to go to the mikveh. In the case of nocturnal emission, one can pour these 9 kavin of water instead of going to a mikveh in order to resume prayer even while still impure, which is roughly equivalent of 4 minutes of a shower, according to certain opinions. However, this ordinance of Ezra was annulled during the times of the Talmud, and this opinion is followed by the Shulchan Arukh. Others say that it is still a good custom to pour upon oneself these 9 kavin of water.
