dipping in vessels as far as a mikve/goes is a problem

טובל בכלים dipping in vessels as far as a mikve/goes is a problem/ The major problem comes from the fact that a lot of mikvot are made with a separation between the concrete structure of the mikve and the ground. But this problem would exist anyway [even without that plastic that they put between the walls of the mikve and the ground]. Though I admit is is hard to imagine how all women would go to the sea after their period. One might make a mikve with a thin layer of concrete such that if it would be pulled up it would fall apart. [That would make the mikve ok since that concrete structure would not be a vessel.].

I am tired when I get back from the sea so i is hard for me to learn Torah this minute. So I thought to take a few minutes to explain a very important aspect of all this. A separation between one's body and the water is only a separation is it is  רוב הגוף ומקפיד stops the water from touching most of the body and one wants the water not to touch. If the clothing stops the water from touching only less than most of the body and one wants the water not to touch that makes the dipping not valid by a decree from the sages. but what you usually have with clothing is the water touches all of the body and one does not mind. that is not even a decree. So a woman can go to the sea with her regular swim suit even during the day of the seventh day and that is a valid dipping--if she dips in all of her body including her head.

i mean to say that if the period is less than seven days [which is usual]then she goes into a natural body on water even during the seventh day and becomes pure at night. but in the unusual situation that she sees again  after that then she waits a day שומרת יום כנגד יום and  goes again into water. If again she sees then again waits a day and again into water. But if she sees for three days then that is a zava and she  needs seven clean days --that means to check on the first day and seventh. If all those days are clean then she goes into a natural body of water But here I have again a problem because at that point she needs a spring. Not a river, nor even the sea but an actual spring. מים חיים   [well as rivers are concerned, that is an argument among the rishonim since rivers are fed from springs underneath them.]