The Ban Tha Sathon hot spring (บ่อน้ำร้อนบ้านท่าสะท้อน) is located in Tha Sathon subdistrict, in the southeast of Phunphin district, Surat Thani province. When coming from Tha Kham (Phunphin) town, one has to take Thai highway 401 to the west, and then the 4448 going south. Some kilometers after crossing the railway one has to turn into a narrow side road to the right, and after some more kilometers turn into another one to the left. Don't worry, it has signs at these two intersections. The compound itself then cannot be missed anymore, one will see the above sign and then directly hit the parking lot.
Already visible from the road is the big pond, which seem to be quite popular for Thai children to do bathing. The water seems to be very clean, the whitish color probably comes from the minerals from the spring. Next to the pool is a building with the sanitary facilities, and as usual in Thailand there are food stalls next to the parking lot as well. The whole compound looks very new, which is probably the reason why I haven't been able to notice it in either Google Earth nor PointAsia yet. We only visited that spring while we were on the way to Khao Sok, so we had neither bathing suit with us nor enough time to check out the swimming ourself.
The pond is filled with water originating from the hot spring, which is encircled with a wooden walkway. Getting closer to the water there isn't recommendable, as it has a temperature of about 70° there. Quite odd to see even a little bit of steam on a sunny day with an air temperature of around 30°. Sadly my Thai is not good enough to get anything of the geological details of this spring from this website, but as there's no volcanism in that area the water must come from rather deep to get that hot.