I have 2 plants 17 days in flower atm. 1 1/2 ft tall in 10" pots. They start in peate pellets, then move to 4" pots, then 6" pots, then 10" pots to form nice root balls yet still leave room for growth. My plants suck down 1/2 gallon every other day give her take. If your leaves are drooping, its either over or under watering. If your letting it go even longer, chances are they're thirsty. Let em drink, then add another decent cup or two full of water tomorrow.... see what moist soil for 2 or 3 days does. If they dont perk right back up....................... dont water them anymore. Though, its my expierence, when they droop... if they're underwatered after a few days the droop goes into crunchy leaves as well... and THAT ya dont want. Everyone says to let your pots go dry, but I prefer to keep the soil just a lil moist. When the topsoil gets dry about 2-3 inches (just feel it w/ your finger, its only dirt ;p) water. I dont want them to stop drinking, they need lotta lotta lotta h2o to grow into strong gals........ so i can cut them down and burn them ;p

Peace. Hope that helps.

PS. a month into veg sometimes lower leaves will die off naturally... to make way for new growth... also on some strains (my calio did it to me which made manicuring a breeze, they just start dropping off like flies too).