One of the most important factors in keeping happy and healthy carnivorous plants is correct watering. Here, I will take you though the different genus' of carnivorous plants and give an overview of what the plants in that genus prefer. Of course, there are exceptions to these rules, some of which I'll talk about, but in general, these are what the plants prefer.
Use distilled water only! Using water that has nutrients in it can lead to a build of up nutrients in the soil which will kill your plant by rotting its roots.
Nepenthes - Tropical Pitcher Plants
Tropical pitcher plants do not like to sit in water for a long period of time. I prefer to keep them in plastic containers with holes in the bottom, sitting in a shallow saucer.
Water from the top until water starts coming out the bottom of the pot and into the saucer. Fill the saucer so that the pot is sitting in about a half inch of water. Let the water evaporate before watering again but don't let the soil dry out.
Pinguicula - Butterworts
This section focuses only on Mexican Butterworts.
There is some debate on how wet butterworts like to be, some people allow them to dry out almost entirely before watering again while others keep them wetter. This is what has worked best for me.
Have your pot of butterworts sitting in a tall saucer. Fill the saucer about halfway up the pot, for me that is around 2 inches. Let the water evaporate until the saucer is dry and let it sit dry for 2-3 days before watering again.
During winter dormancy:
Depending on your species, some need to go through a dry winter dormancy period. An example of this is with P. gypsicola where, once it starts to show signs of forming its winter leaves, you need to keep it bone dry. Once it starts to show carnivorous leaves again in spring you can slowly start watering it.
Drosera - Sundews
There are many different types of sundews varying in size from a dime (pygmy sundews) to forming large bushes such as the forked sundew.
Keep them wet, always sitting in a few inches of water, and don't let them dry out.
Utricularia - Bladderworts
There are 3 types of bladderworts with different water and soil needs and I'll walk through each of them separately here.
Terrestrial Bladderworts
U. pubescens
Always keep terrestrial bladderworts sitting in at least a half inch of water. I typically keep mine sitting in two inches of water, let it go down to about a half inch, and then refill. Don't let them get dry!
Some terrestrial bladderworts such as U. cornuta and U. praelonga appreciate occasional flooding.
Epiphytic Bladderworts
Epiphytes are plants that grow on the surfaces of other plants such as on trees. Because of this, these carnivorous plants often have reduced water needs (compared to terrestrial bladderworts) and prefer to grow in primarily long fibered-spaghnum moss.
There is more variation in the watering needs of these bladderworts. Some, like U. alpina prefer to sit in only a thin layer of water (around half an inch). Others such as U. humboltii prefer to be very wet. I keep the water level at the pot level, letting it drop only about an inch between watering.
Always keep these plants sitting in water and don't let them dry out. For more specific watering instructions, check out the Utricularia section on my website.
Aquatic Bladderworts
U. gibba
As the name suggests, these plants prefer to grow submerged. I typically plant mine in a pot filled with peat moss and topped with a thick layer of sand (this prevents the peat moss from getting washed out). I then place this pit in a large container, such as a fish bowl, and keep it constantly submerged.
Dioneae - Venus Fly Trap
The most well known of the carnivorous plants, the Venus fly trap prefers to stay wet but not sitting in as much water as some other carnivorous plants.
Keep it sitting year round in about 1 inch of water. Do not let them dry out
Heliamphora - The Sun Pitcher Plant
Sun pitcher plants have similar water requirements as Nepenthes but prefer to be slightly drier.
It is best to used chilled water (I keep a jug in the fridge for my heliamphora). Water them from the top until water comes out the bottom and creates a thin layer in the saucer - do not let them sit in water for long.
Let all the water evaporate and allow the plant to sit with no water in the saucer for around a day before watering again. Don't let the media go dry.