I've started using the swimming pool at the local community centre. To get in you have to walk through a waist deep pool of water - their version of a pre swim shower. The pool itself is 25 metres long, and at its deepest point it is 1.3m deep, but only 1.1m at either end. So obviously there is no diving. Also, there are no lane ropes, or flags to mark 5m from either end, so doing backstroke is a little slower at the end of a lap than would be in a more equipped pool.
However, entry is free. You walk in, ditch your stuff in a provided basket and walk through the 'shower'. Then you have to sign a scrap of paper an old man proffers and then you can swim. I think the water is untreated - I certainly couldn't smell any chlorine, or taste any salt. There were a couple of 'ojiisans' (grandfathers) gardening around the edges, and 1 of them told me I was the first swimmer of the season!