Have to press down hard for keys on keyboard to work?
The link provided in the comment has good advice, but not everyone can take their Apple gear to a professional — this is especially true if you live in a country that does not have an Apple Store or do not live in a larger city. 

So, if you can't get your laptop to a professional, then you'll have to take care of the keyboard yourself until you can. 


Double-check your keyboard settings in the System Preferences, you
mention "slow keys" but there are two settings in there: "key repeat"
and "delay until repeat" which affect the timing of keystrokes to
response.
Hook up an external keyboard (any USB keyboard will work, though you
may loose some Apple-specific functionality if using an non-Apple
keyboard). Pressing extra hard could cause more damage and further exacerbate
the situation you already have.
Get a repair guide from a site like ifixit.com which will show you
how easy or difficult (it's usually on the difficult side) it is to
remove and replace the keyboard or at least get to it for a closer
look to find a hardware cause. This will help you to clean,
dehydrate, and reassemble you laptop as the linked comment suggests.


Depending on what was in the water and how much of it was spilled and how long before cleaning under the keys took place, you may have a corrosion problem where the residue left behind after the liquid evaporated is gunking things up.