Spa water by the Danube

I took one of my lads to his football match in the north of Pest this morning. Whilst waiting for the game to begin I walked on the nearby embankment of the Danube for a while, there is a drain there that enters the river and where the waters meet birds gather. There were Black-headed Gulls, Mallards, Coots and a fine drake Northern Pintail. A Great Spotted Woodpecker called in a nearby patch of trees, too. But the real highlight there was this... Another drain, which comes from a spa baths, enters the river close by. The water must be quite warm as steam rises from it. As it comes out of a pipe it collects in a concrete basin on the river bank before then passing through another pipe into the river. And there, in this basin, was a man. He was lounging, basking in the warm water, having a free spa bath, wearing a denim cap, his clothes on the bank nearby. Iventive maybe, but I wondered what is in that water ? Is it clean water from the spa being allowed to escape ? Or waste water ?