Agreed.
In fact, I only learned this during my second EOM (Election Observation Mission) in Bosnia, in November, 1997, when my superior (who was a highly decorated ex-paratrooper), stressed the importance of consuming sufficient quantities (volumes?) of water - he recommended two litres a day, - especially during winter when you might not feel the need to keep hydrated.
I was astonished, but have (to a large extent) heeded his advice ever since.
And - and I doubt that this is a coincidence - my sinuses have rarely troubled me to quite the same extent, since. In fact, whenever I get a bout of sinus troubles, I realise that I have (inadvertently) cut back on water, and simply consume more water, preferably mineral water.
A glass of water nearby while I am working on the computer; a glass while I am sipping coffee; a glass - always - beside my bed.
Now, this doesn't cure sensitive or troublesome sinuses, but it does alleviate and ameliorate the agony they can cause; another recommendation of mine is to (always) have some Olbas Oil to hand; a few drops on a pillow, or on a tissue (and inhale) also ease symptoms.