It depends to some extent on what your source water is like to begin with. There is nothing wrong with being over-cautious and preparing water ahead of time if you have questionable source water as some here seem to have. I have been filling with the Python direct from the tap for over 25 years now. The parameters are the same (zero GH/KH) and there is only chlorine (not chloramine) in my water. I change 60-75 sometimes even 80% of the tanks this way. I have tanks of wild caught fish that have lived into and beyond the normal expected lifespans, spawning regularly (fry sometimes evade predation). If I had harder water, and/or chloramine added, I would probably be doing things differently. But I would also not have a room full of tanks without the Python. When I acquired my first larger tank (a 90g) in 1995, I asked the store about water changes and they put me on to the Python and I have never looked back.