Once in a while the oatmeal gods yield up watery oatmeal, precise though we may be with our measurements.
I found a cool trick: top with granola! Stir in just slightly. It absorbs quite quickly.
Flax seeds (if you buy the vacuum packed stuff and store in fridge so it doesn't go rancid) are delicious and healthy in oatmeal, and absorb like a charm. Wheat germ, too.
I'm also starting to get into stirring yogurt into oatmeal...quite thoroughly. Gives a nice light texture (and flavor if it's flavored yogurt) and will also make the wateriness moot.