I agree with waterdawg. I lift each pot to determine when a plant needs water, this will tell you accurately when to water. When a container is "light" or on the verge of being completely dry and the plant is still perky, I usually water at that point. Plants will survive even if there is no moisture left in the pot, however, if you run a all natural set up there is a point where not enough water can be detrimental to the health of a plant. Much of the microbial life found in healthy soil will rely on super tiny microscopic droplets of water that cling to soil particles, plants don't use this water. I often take clones and root them in cups, from time to time I accidentally let the dry up completely. The roots will be dry and brittle while the plants/clones remain healthy and lush, no drooping or anything. In my experience it is plant dependent but some plants will begin to wilt after a matter of hours of having absolutely no water to soak up, some plants will go a full day and sometimes multiple days with zero moisture in the cup. In most cases if the clones were taken from a healthy plant, the dried up clones will bounce right back, even after they have wilted, appearing to be dead. Ive got one male in my garden that I have let die fully in a container, dried up plant, no lush green to be seen. Gave it a small drink of water and one shoot came back to life(which means the plant was actually still alive).
I always split up my watering doses into two or three separate doses, depending on how established a particular plant is; newly transplanted plants usually get three, fairly root bound plants will generally get two because they soak up the water and distribute it throughout the soil/root ball much faster and easier. If I was watering a three gallon container(typically 3/4-1 gallon of water I would water once with around 1 cup of water, wait 5-15 minutes, then give one more cup, wait 5-15 minutes, then give the remaining water. Doing this will assist the soil is drawing in fresh air and also will help distribute the water more evenly throughout the medium.
I derived this technique from a Japanese bonsai growing book I picked up at Hastings a few years ago.. "Water once for soil, once for the roots, and once for the plant" Its not necessary to take it to that extreme but at the very least, watering twice is far superior than trying to soak the entire root ball all at once. Experiment a bit, you will see why I feel this way.
On another note, some plants don't like to be allowed to dry out as much as others. Some of them just prefer more stable moisture levels. My Panama Red is like this, only after becoming very established in a container will she tolerate extended dry periods. Took me awhile to realize that but after experimenting a bit, it was clearly obvious to me how she needed to be handled to keep healthy and vigorous. Similar to a citrus tree and things of that nature.
In short, I recommend trying to developed a sense of container weight to determine when to water. From there experience will reveal all the little tips and tricks in between to take it to the next level.
If you are having trouble figuring that out, simply place a dry container of soil equal to the size of container your plants are in. Also place a container that is heavily saturated with water next to the dry one. Lift them often to compare and troubleshoot. Small learning curve but its worth the time and effort to learn IMO/IME.
...haha j/k man, I'm still learnin too...and you're absolutely right about that, it will become stagnant and get bad bacteria in it that will cause root rot and other disease...I can't express enough about not letting your girls "set" in water...they do need to dry out for oxygen to get to the roots, but not for too long, mine are dry for a day and then I water/feed...and about feeding, as soon as those lil round leaves are wilting ((cotyledons=food/energy for younglings)) usually about 3-4 weeks old, it's time to start 1/4 strength nutes and work your way up to full strength from there...hope this helps man...
nice job...looks like a kushy bag bean there 
nice and frosty already...remember it's not ready until those hairs recede to nothing and are replaced by swollen calyxes 
good luck and my only suggestion would be to veg longer, wait till the nodes are staggering instead of right across from each other and little branches start to form in those staggered nodes and throw her into flower, trust me you will be much happier about what you get in return...and it doesn't take that much for 1 plant, when I did CFLs I used around 150w per plant and did great...now I use HIDs and do much better 
peace bro...
