Low milk supply?

Question

I’m a ftm so I’m not really sure on these things and wanted to get clarification on this! 
My LO is ebf and I usually have atleast one bottle a week that has been pumped, and save it in the fridge for when I go grocery shopping so my husband can feed him.
Well my husband fed him while I was away and I decided to pump when I got home since I skipped a nursing session and like I said above, I like to keep a little milk in the fridge in case I need to go anywhere. 
Well when I pumped it had been like 4ish hours since the last time I had nursed him and I only pumped 2.5 oz... total!
all the other times I pump I usually go longer without nursing him and get a lot more so this is a first that I’ve pumped in a shorter time span. 
2.5 oz just doesn’t seem like a lot to me at all and now I’m worrying that my milk supply has dropped or is low. I know that pumps aren’t as good as getting the milk out as much as babies are but still.. 
he usually goes 2-3 hours in between feedings.
I know I haven’t been staying as hydrated as I should (I know shame on me) but does that have anything to do with your milk supply? Because I’ve heard that it does & doesnt..

Answer

So I pump when I’m gone in the mornings, I miss one feed so I pump once, and I usually don’t get a lot and it takes a while. I was worried that my supply was going down but he’s ebf otherwise and on the four days a week I’m not gone in the morning he eats fine so I think it’s just pumping honestly. I wouldn’t just chug some water and wait to see if you see a change in your normals nursing patterns with him.