A mikva or mikveh is a place used for ritual immersions. In general, if there are more than 40 SE'AH, then the remainder of the water may come from any source.
Many synagogues also provide indoor mikvas.
The FAQ is a collection of documents that is an attempt to answer questions that are continually asked on the soc.culture.jewish family of newsgroups. It was written by cooperating laypeople from the various Judaic movements. Hopefully, the FAQ will provide the answer to your questions. The FAQ maintainer will endeavor to direct your query to an appropriate individual that can answer it.