We got a question on the Kumamoto-i mailing list about pools in Kumamoto. I responded with a map that shows the location of public pools and fitness clubs that have pools:
https://groups.yahoo.com/neo/groups/kumamoto-i/conversations/messages/12822
By the way, one really unique pool is in Kashima. It’s unique because it fed by natural spring water . . . and very, very cold. (I wouldn’t recommend actually trying to swim there until August and even then you may find it hard to stay in the water very long.)
Check out the following blog post for more information, including a map:
http://bunkaseminar.blogspot.jp/2012/05/spring-water-tour.html