Lily is right. That isn't too much, check for leaks just to be sure. Especially in a dry climate or when you have an A/C (or heater) in the house running.
You can fill for evaporation with fresh treated water anytime so you don't have to see the tank look empty. Also still remember to do pwc
because you still need clean fresh water for the fish, plus minerals that the new water provides are generally beneficial and you still need to take out old build up ones. It helps keep your tank healthy.
New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?
Start here - Aquarium Advice Article
FW Favorites right now Clown Loaches, any shrimp - SW Vase Red Mangroves