My split A/C unit doesn't drain much water
You need to find out why the cooling efficiency is slightly lower. Offhand, I'd guess it's a clogged filter. 

If it's low on gas, it will freeze up the coil and produce less water (and not work very well), but a whole bunch should come out when it shuts off and melts This should happen within a few minutes, so don't walk away, while you: 

Let it run for a good while, and then set the fan to on and the A/C to off; what happens? If lots of water starts coming out, you're low on gas and your coil is freezing up.

You can confirm this by removing the panel from the coil, and you'll see it's all froze up. Seeing frost on the 'fat' line (at just outside of where it enters the coil) is a good indicator, too.