Before building a water station, I would make water as soon as I used the last water then let the new water sit until I needed it. I would toss a heater and pump in for an hour or so before using it and never noticed an issue. As long as your container and water are clean, I do not think there is much that can go wrong other than possibly some of the trace elements settling and binding to the container unless you are using something with antibiotics, in which case the antibiotics would just be useless but the water would otherwise be good.
Now I mix water and leave it on a timer to circulate and heat the water 15 minutes every hour. I never fully empty the container unless I am cleaning it, which I do every few months.