Some houseplants, such as succulent plants (e.g., cacti, aloe), need little water and will continue to thrive while you are on vacation. However, many other houseplants need more consistent waterings and if you're going on vacation and don't have a friend or family member to come water your plants, you may have to have an alternative plan. Before you decide that you don't need to worry about it, consider how long you will be gone and how often your plants typically need water. Remember, if your house is going to be warmer than usual, your plants will need more water than usual and if it is going to be cooler than usual, they may need less water than usual.
Give the houseplants that need water often a good soaking before you leave. Water the plants slowly and until some of it seeps out of the bottom drainage holes. Throw out that water because it may contain excess salts that build up in the soil. If you're only gone for a few days or even a week, this last watering may suffice for most houseplants while you're away. However, for heavy drinkers or if you're going to be away for a longer period of time, also choose one of the following methods.
Fill containers with water and set the plants in it. The pots must have drainage holes in them for this to work. For large plants and heavy drinkers, use larger containers and for small plants and light drinkers, use smaller containers. The plants will absorb the water from the bottom as the soil dries out. This is not a permanent solution, but will work well while you are away on vacation.
Create your own watering wick. Take a plastic bottle and fill it with water. Then quickly flip it over and stick it several inches into the soil. Choose an area of your soil that does not have a lot of roots so you don't damage them. The size of the bottle depends on your plant's needs and how long you'll be away.
Purchase and use a commercial product designed to water your plants while you're away. For example, a commercial watering wick has a long neck with a rounded top. Just like the homemade version in Step 3, you fill it with water, flip it over and place the long neck in the soil. A commercial capillary mat is similar to the containers as described in Step 2, and available in several varieties. For example, some have tank-like bottoms with small holes on top that slowly seep out water onto a fabric cover. The plants sit on top of the fabric--which is constantly moist--and absorb water through the drainage holes.