Is it normal for liquor to randomly be watered down

I had 2 liquor bottles in my closet. One vodka and one rum. The vodka tastes kind of the same but the rum really tastes watery and weak. Its been a week that i brought it. It tastes weaker. The collor is the same and i saw no water particles inside of it. I think its kind of weird. I also didnt feel so drunk after drinking it. I drunk about 3/4 mount full of it. And i wast any more drunk that almost tipsy.is this normal?