Planning a vacation doesn't necessarily mean you have to get someone to come and water your plants, especially if you only have a few that need a little care while you're out of town for a few days. Just grab a platic water bottle and a couple of plastic pot trays to rest your plants in. By the time you're finished, your plants will water themselves.
Just grab a few cheap plastic pot plates for your plants and for the water bottle, put each of your plants in a plate, and then connect the plates with the one you'll use for the water bottle with a a piece of rubber tubing, cotton string or cloth. Then put the cap on the water bottle, drill a small hole in the bottom, and fill the bottle with water through that small hole. Turn it upside down and put it in its own pot plate.
As long as your tubing stays unclogged and full of water, and the tubes are connected to each pot plate, the bottle will only drain as much as the plants in each connected pot plate can absorb. The system is completely self-regulating, and requires no motors, power or human intervention.
If you have a lot of plants, you can do the same thing with a single large tray where the bottle rests in the same tray with the plants. You do have to be careful of the type of soil you use with your plants — if the plants you have don't take well to constantly-moist soil, they won't like this solution.
Instructables user gkaneto outlines the process in great detail at the link below, complete with diagrams, and some alternatives if this doesn't work for you. Give it a look the next time you're planning an out-of-town trip and thinking about how your plants will survive your absence.
How do you keep your plants happy and healthy when you're out of town? Share your self-watering tips in the comments below.
Self-Regulating Watering System [Instructables]