Is a pool allowed to be used as a mikvah for keri, for erev shabbos, and Shabbos day? If so does the filter have to be off? Since it is not only made of rain water i am having a doubt. Please answer in a chabad or chassidic point of view.
The Gemara writes in Brachos
ת"ר בעל קרי שנתנו עליו ט' קבין מים טהור בד"א לעצמו אבל לאחרים ארבעים סאה ר' יהודה אומר מ' סאה מכל מקום ר' יוחנן וריב"ל ור"א ור' יוסי בר' חנינא חד מהאי זוגא וחד מהאי זוגא ארישא חד אמר הא דאמרת במה דברים אמורים לעצמו אבל לאחרים מ' סאה לא שנו אלא לחולה המרגיל אבל לחולה לאונסו ט' קבין וחד אמר כל לאחרים אפילו חולה לאונסו עד דאיכא מ' סאה וחד מהאי זוגא וחד מהאי זוגא אסיפא חד אמר הא דאמר רבי יהודה מ' סאה מכל מקום לא שנו אלא בקרקע אבל בכלים לא וחד אמר אפי' בכלים נמי בשלמא למ"ד אפי' בכלים היינו דקתני ר' יהודה אומר מ' סאה מכל מקום אלא למ"ד בקרקע אין בכלים לא מכל מקום לאתויי מאי לאתויי מים שאובין
The rabbis learned in a baraissa: A baal keri who had 9 kav of water poured on him is Tahor. when are these words said? (when he wants to daven or learn) for himself. But (if he wants to daven or learn) for others, 40 seah is required. Rabbi Yehuda said that 40 seah is always required. Rabbi Yochanon and Rabbi Yehoshua Ben Levi, and Rabbi Elazar and Rabbi Yosi Ben Rabbi Chanina: one of this pair and one of that pair argue concerning the first part of the baraissa. One of them said: Where the baraissa qualifies “when are these words said? for himself, but for others, 40 seah is required,” that is referring to a sick person who has regular marital relations, but for a sick person who sees keri accidentally, only 9 kav is required, and one of them said: for others, even a sick person who sees keri accidentally, it is not sufficient unless there is 40 seah. And one from this pair and one from that pair argue concerning the last part of the baraissa. One of them said that that which Rabbi Yehuda says that 40 seah is always required is only where the water is in the ground, but if the water is in a vessel, it will not work. And the other one said that it works even in a vessel. According to the one who says that 40 seah works even in a vessel, it makes sense that Rabbi Yehuda learned 40 seah is always required, but according to the one who said taht 40 seah works only in the grand but not in a vessel, what does Rabbi Yehuda add by saying ‘always.’ He means to include drawn water.
From the end of the Braisa, we see that Rabbi Yehuda says that drawn water is fine for Tevilas Ezra.
R' Shneur Zalman of Liadi (Orach Chaim 88:1) codifies this:
ותשעה קבין אלו אינן מטהרין אלא כששופכין עליו אבל לא כשטובל בהם בין שהם בכלי בין בקרקע עד שיהיה ארבעים סאה (בקרקע) ואז מועילים לטבול בהם אפילו לבריא ששמש מטתו אפילו הם שאובים These nine Kav only purify when they are poured, but not when one dips in them, unless there are forty Seah in the ground. [Once there are these forty Seah], even a healthy person who had relations may dip in them even if [the water] is drawn.
For Keri a pool can be good enough since it satisfies the Takkanas Ezra, as mentioned above. For Hosafas Kedusha you would need a real Mikva.
It is possible to make a pool Kosher. If you allow at least 20 Sa'ah of rainwater to collect before adding the rest, and if the faucet is higher up -- causing the water to flow along the bottom before reaching the rest -- it can be Kosher.
For normal mikva (daily/erev Shabbos/shabbos) if you don't have anything else, you can use it, and it's better to have the filter off being that it's not mandatory from the Torah. As for mikva that is mandatory it needs a proper mikva. If you don't have one, maybe you should go to a pool in the mean time (not so sure), but it won't make you Tahor. Just to point out, in Camp Gan Yisroel around the world, if there's no lake or mikva, people use a pool.
From DailyHalacha.com (a sephardic website): http://www.dailyhalacha.com/m/halacha.aspx?id=1215
A woman who is a Nidda can divest herself of this status only by immersing in a Halachically valid Mikveh, which is defined as 40 Se'a of naturally collected rainwater, that had not been drawn from another source. This means that a Mikveh must be constructed in such a way that rainwater falls directly into the Mikveh. If the water is brought to the Mikveh from somewhere else, either through human involvement or a piping system, it is invalid, and a Nidda who immerses in such a Mikveh is still considered a Nidda.
For this reason, Chacham Ovadia Yosef rules (in Halichot Olam, vol. 5, p. 143) that a swimming pool may not be used as a Mikveh. The water in a swimming pool has the status of Mayim She'uvim – "drawn water" – and is therefore ineffective in ridding a woman of her Nidda status.
When Chacham Baruch Ben Chaim Z”L served as Rabbi in Salsbury, South Africa, he sent a letter to Chacham Ovadia Yosef asking if he could permit the women in his community to immerse in swimming pools, given that no proper Mikveh was available. He noted that if he would not permit women to immerse in swimming pools, they would resume relations with their husbands without immersing altogether. Since pools are disqualified for use as a Mikveh only Mi'de'rabbanan (by force of Rabbinic enactment), perhaps it is preferable to instruct women to violate this provision, and immerse in pools, so as to avoid their violation of the far more grievous transgression, of relations during a state of Nidda.
Chacham Ovadia replied that a Rabbi may not allow people to commit a Rabbinic prohibition even in such a case, where they will otherwise violate a Torah prohibition. Halacha does not become more flexible in response to the "intimidation" of those who are prepared to transgress Torah law if a Rabbinic provision is not suspended. This principle is explicitly mentioned as well by Rabbi Moshe Feinstein (Russia-New York, 1895-1986), in his work Iggerot Moshe (Yoreh Dei'a section, 52; listen to audio for direct citation), where he writes that a Rabbi may not allow a violation of Halacha of any kind due to the threats of sinners that they will otherwise commit more grievous transgressions.
Chacham Ovadia added another factor, as well, namely, that issuing a ruling permitting the use of pools as a Mikveh eliminates any incentive on the part of the community to construct a proper Mikveh. For this reason, too, a Rabbi must not issue such a ruling, and should rather insist that the community take it upon itself to construct a valid Mikveh.
Summary: A swimming pool may not be used in lieu of a Mikveh, even if no proper Mikveh is available.
It really depends on why one is using the Mikvah, and "Men's Mikvah" doesn't help (other than to eliminate Nidah). For many, it is simply because there is an 'Inyan' and Mitzvas Anashim M'lumadah. In the absence of any clear reason why one is doing it, it would be very hard to pin down what Mikvah is acceptable. Specifically, without being very welled versed in Hilchos Mikvaos and clearly understanding the reason, it is impossible to evaluate what leniencies can be relied upon in defining a Kosher Mikvah.
Here are several possible reasons why a Mikvah may be used, and their implications in regards to a pool.
[For Nidah & Geirus most pools are probably useless for a variety of reasons.]
For Tevilas Ezrah (Keri), even a shower of Tisha Kavim Mayim She'uvim (9 kav-units of drawn water) is generally agreed to be enough (for example, see here Answer 1 or here). There is a chumrah to use a mikvah to adhere to other views on this matter, and Kabalah. Therefore it would seem that one could use a pool, though maybe not if one wanted to adhere to all the views.
There is an often cited reason from I-forget-who that if a Mikvah can make someone a yid, how much more can it elevate someone who is already a yid. To fulfill this, one probably can't use a pool, unless this reason is more symbolic than anything else.
It removes certain types of Tumah. Therefore nowadays, when we are all Tamei Meis, it won't help even if/when it is Kosher.
A Sofer should use it in general and specifically before writing Hashem's name (It is not clear in Halacha the level of Chiyuv; at any rate it doesn't Pasel his Kesivah if he didn't.) Everyone should before the Days of Judgement (Rosh Hashanah & Yom Kippur). Many other reasons to use a Mikvah are given based on Kabalah, in many Seforim and by many Gedolim, predominately amongst Chasidim (and Sefardim?). But for all these, clear rules are hard to come by. One would need to know (1) which Sefer/Gadol one was attempting to adhere to and clearly understand their reasoning, and (2) Hilchos Mikvaos inside out, only then making an informed decision about what leniencies are acceptable.