What is a Mikveh, Halakhically?
The water must originally have been transported to the mikveh in a manner resembling the natural flow of waters. The general practice is to build cement channels at the sides of the mikveh roof, which will enable rainwater to flow directly into the mikveh. Done right the first time, with the required initial amount of water, other piped waters may be added later in whatever quantities and at any time, and the mikveh will still retain its religious validity. The waters must be stationary and not flow (not even the flow caused by a filter) while the mikveh is in use. The water, by all means, should be chlorinated to assure its meeting the highest standards of hygienic cleanliness. (While the chlorinated water may be somewhat discolored, it does have to retain natural water color.) Water deriving from a natural spring is considered a valid mikveh if it complies with halakhic conditions. Also quite proper is immersing in the ocean, where there is no mikveh available, given the satisfaction
