Indoors, there are ways to keep houseplants moist if no one is stopping in to water for you, from Ward Upham of K-State:
• Place well-watered plants in a plastic bag. Prop up the bag with wooden dowels or something similar to keep the plastic off the leaves. Make sure the enclosed plants will not receive full sun, as heat buildup could cook them. Bright, indirect light is best. Plants should keep for about a week.
• Place a dish-drying rack upside down in the bathtub (if the bathroom has some natural light) and add several inches of water to the tub. Push one end of a shoelace through a drainage hole on the bottom of a pot and into the potting soil of your houseplant. The other end of the shoelace dangles into the water. This wick system will replace water in the pot as the plant uses it. Plants can last a couple of weeks if you have enough natural light.
• There are numerous commercial products that can be used to automatically water houseplants. The advantage of these products is that the houseplant does not normally need to be moved. All require a reservoir from which water is either siphoned or pumped to individual plants. Houseplants should last as long as the water holds out.