What is "lots of water"? You post doesn't specify.
Most people are chronically dehydrated BEFORE diving. Add the dried, filtered air and you become even more dehydrated after diving. Dry scuba air, sun and physical exertion will suck the moisture right out of your body. Add a tropical location like Cozumel and likely drinks / dancing / sun / heat / late nights, it is not a mystery why someone becomes dehydrated.
My personal vacation dive plan is to bring a Nalgene bottle with me so I can track how much water I drink in a day. I wake up, drink 32oz to start the morning before I get on the boat. I bring my Nalgene with me filled up with 32oz of additional water. Attach a carabiner to the top of the nalgene so you can clip it off somewhere close to your gear so it is close by. After my first dive, I drink the remaining 32oz of water before my second dive and then another 32 oz after my second dive on the boat ride back. You will probably have to pee every five seconds under this plan but the ocean doesn't seem to mind
After that, I jump in the pool to "desalinate" order between one to ten of those frozen drinks with the umbrella and float around the pool until dinner time. I keep my nalgene bottle close by and drink another 32-64oz of water while relaxing in the pool all afternoon in between frozen drinks.
I drink about 120oz of water on a normal day (10 glasses worth). I am guessing I jack this up to 160-180oz on a tropical dive vacation since there are so many factors working against me.
How many glasses of water did you drink during the day?