They also need plenty of circulating fresh air combined with constant high humidity. Watering Most houseplants like to be just moist all the time, neither bone dry nor waterlogged. Wild variations, such as leaving them till they wilt followed by standing them up to their necks in water for weeks, are the real killer. Watering from above or below is not an important issue because after watering the compost should be moist right through anyway. Make sure surplus water drains away so plants are not left standing in water.
Some plants have more specific requirements.
The urn type of bromeliads need their urns kept topped up, though they don't need to be too damp at the roots. Carnivorous plants like to stand in several inches of water from spring to autumn, but only need the compost kept moist in winter. Orchids should be left to just about dry out at the roots between waterings. However, they do need frequent foliar spraying to keep humidity levels high. Tap water is fine for most houseplants, as they need some chalk.