No need to excuse your phrasing. This is power plant waste water, and it's essentially a pure gold mine for the company. It's very overrated and most Icelanders don't go there unless the ticket is on a reduced price. One thing you got wrong though, yes this is sustainable heat source, BUT, on a geological time scale. The volcanic systems are still active but the heat source is dependent on there being intrusion activity. There can be hundreds of years between eruptive and/or intrusive activity which is not predictable on a smaller timescale. Alas, what this means is that you can drain your the heat source, if you are not careful and pump too aggressively. There are many other things to mention but I leave it for now. Otherwise quite accurate video 🙂