I used to drink water only when thirst climbs up my throat; over the course of last year or two, I gradually increased the frequency and amount of water intake, to about 2.5 liters per day. Not an extraordinary amount, but quite effectively, it has alleviated my chronic stuffy nose.

Slowing down aging, improvements of digestive system, etc. I can't really feel. But the freedom to breath through my nose, which used to occur only after a hot shower, to be liberated from having to gape my mouth like a dazed cat all the time, is a huge reward in itself.

Anecdotal, of course. But I've rule out tons of other variables already (location, allergen, air humidity, temperature, diet, etc.) for this chronic---and inherited---condition, and I'm reasonably confident in my uneducated guess that hydration has something to do with it.