I'm thinking any healthy plant can go four days after being given a extra dose of H2O.

Water them, get them out of your head and enjoy the lady in lake eh.

Or...if its really that much of concern to ya,

http://www.littlegreenhouse.com/accessory/garden.shtml

That or create a small plug, or a tight seal, for a small diameter line of hose to be able to super slow style drip on your plants from the bottom of a water source above the soil line. And for sure only work with plain, un fertilized water.

Those each were what I was wondering when I decided the plants, and myself, would be okay to give them a good drink before I went away for a weekend here and there the first couple times I wasn't around to tend to their scheduled feeds.