Firstly, you want to hope that was clean water, no sugars, no coffee or tea or juice etc!
It's a large area to dry properly but even though you might think it's dry, it's probably not yet, you may want to consider trying the following:
Place the laptop near a dehumidifier (preferably near the intake) to try to draw out water for several hours
Place the laptop in a highly air conditioned room, aircon removes moisture from the air, you may need to place a fan blowing air over the unit to encourage the water to become airborn
Place the unit in a sealed bin bag with a lot of salt or dry rice in it (be really careful not to get this on or in your unit, salt water will corrode your laptop like thing else, put the laptop on a cardboard shelf over the salt/rice)
If you have a load of silica gel bags (they come with loads of things, I got a particularly big one with an iMac once leave them on the keyboard and seal it in a bag to try to draw moisture out. (Top Tip, keep a bag with silica gel bags in it, whenever you get one in something, save it!)
All of the above may take several attempts to work, or may simply not work.
Finally, you can disassemble the keyboard unit, this may be to try to dry it further, or to replace if it turns out to be broken, it's not too difficult a job, lookup your model on iFixIT.