MOST IMPORTANT: Carnivorous Plants require water that is very low or completely absent of dissolved solids. In terms of ppm, <30 or better is needed. Pure water promotes a stable pH and a nutrient free root zone. Water that is reverse osmosis purified or distilled is most suitable. Fresh rainwater can also be utilized.
The "Tray Method" is the most common way to water Carnivorous Plants. Carnivorous Plants benefit from sitting in a shallow tray that is periodically filled with distilled water. Most Carnivorous Plants should be watered "from below". This method of watering will work well for most all Carnivorous Plants as long as specific watering regiments are followed.
A Butterwort should be watered twice every three weeks during the growing season. During the winter the plant should be watered much less. Maybe once a month depending on the size of the pot and the plants' exposure to sunlight. The rule of thumb for a Butterwort in a peat moss based media is water less than more.
A Sundew should be watered twice a week during the growing season, never allowing the tray to dry completely. During the winter they can be damp but not waterlogged. If you live in a high rainfall region you will need to empty the tray periodically to avoid a saturated soil condition.