For primary, all I usually do is just putting lid loosely on my tank. Without snapping it in place. Worked for me like a charm. Huge amounts of CO₂ will blanket against air pretty well. Just be advised that it is a risk. A little one, but one none the less. Make sure there is no way lid gets thrown off your tank by accident, no way dust to get blown inside, things like that. And try not to disturb CO₂ blanket by moving tank around.
If I know that fermentation will be slow, I use lid with a hole in it. I put it tightly on. I put a gauze (medical sterile one) in the hole, and cover it with a tinfoil. It's enough to release CO₂ and keep away bad guys. Less problems than with having liquid over my beer.
Most common advice is to use a lid with hole, and rubber cork with airlock in it, like this:
You can do it, it will work, but I leave it for secondary. You can drill it yourself, you can (probably) buy already drilled. Fastest and not so expensive way is to buy lid, cork and lock together, you will know it will fit. I discourage drilling by your own as it is easy to get that wrong.
Oh, and don't put water there. Microorganisms like water and you don't like them next to your beer. Use vodka or something like this.