How much to water.

Your going to want to be really careful on water and remember the golden rule. Better to under water than over water. My plants look like I just kicked them in the balls after I water them and scare me, so I do it every 3-4 days now depending on evaporation ratio.

Dude.......it if aint broke, don't fix it! Just my opinion though.

From what I have read, over watering is a big killer so go easy man. If you're plants are looking green and healthy, you're prob doing it right.

If you really want to be sure when to water, maybe invest in a cheap soil moisture meter. That's what I'm gonna do for my grow.

What SnowWhite said is correct, I believe the way you are doing it now is the best. My logic: when the soil starts to get dry the plant slows down its growing, since it knows that to survive it needs water so it starts to save on drinking water and slows its H2O absorption rate. Therefore, I let my babies get unaroused (their arms flop down) before watering.
Finally, when you give them water they will start acting like a happy guy on ampthetamines, since now, with plenty of water they start absorbing water at a tremendous rate. This will cause the plant to grow, to get stronger and more healthy in case of another drought. Hey, it's just my opinion.

The main answer to your watering question is, water when your pot it totally dry, all the way to the bottom, and when you water, water very evenly, and thorough, all the way to the bottom. it can take more than 3 days for a pot to dry, sometimes 1 week. when your plants are flowering usually they have rooted the pots out all the way and will drink like maniac's, and by expierence usually need watering every three days. invest 5$ in the moisture meter, it really is great..