I try to temperature match the water going in with my tank now and it usually only drops from 26 to maybe 24/25. I used to use cold water only and fill up slowly and the fish would be ok(over the summer months) but I had an incident one day quite recently. I believe the cold water went in too quickly and the temp plunged and all of my fish were not happy. They honestly looked like every single one was a goner. I was lucky to only lose one of my green tiger barbs that day (although it didn’t feel like it at the time, he was my favourite of the school I have). In hindsight I was lucky not to lose my entire stock that day. I have temp matched ever since. I don’t have to have it exact but anything over 24 and under 26 should be completely fine (the tank will end up somewhere in between 24 degrees and the 26 it usually sits at which isn’t much difference. Don’t try to fill the tank back up too fast. Fish are pretty resilient to less than ideal conditions for a surprisingly long time as long as the changes aren’t so fast it shocks them.