You have to use water. It's what the plant uses to make food (look up the equation for making glucose). You can add nutrients to the water to make it grow faster/healthier if that's what you mean. But nothing is going to increase it's potency. That's genetic.
For seedlings you want the soil to stay damp. After you get your first real leaves you should let your soil dry out between waterings. Stick your finger about an inch or so into the soil and if it feels wet, don't water. When it needs water, water thoroughly until you get runoff. You should check the PH of the water before you add it and compare that to the run off. If your runoff PH isn't where it should be, adjust your water's PH until it is.