There are some reminder apps to help you keep track, if that's something you would be interested in. There are ways to estimate you hydration needs, but I would advise not to get to hung up on that.
There's also the true and tried method of always having a water bottle with you. Sip by sip, you'll be drinking more water without noticing. That's what I do, I have a 500ml bottle with me at all times. I got to a point where pure water makes about 80% of any liquid I ingest - I can't pass the morning tea, and a glass of chocolate milk after a run is like nothing else. It's been a few years since I ordered any drink other than water at a restaurant. When I feel fancy, I order sparkling water.
And it doesn't have to be water. Tea is basically water with whatever taste you like - try not to add sugar, but go for the lemon and milk. Juices are also mostly water - again, hold the sugar, easier because most fruits are already sweet enough on their own. A watermelon, as the name indicates, is around 90% water. Eat it and you are basically munching water. Most fruits have a high enough water percentage to help you hydrate.