I have gone three or so winter months without watering my Mexican Pinguicula with no ill-effect, however I have also unintentionally left plants without water for too long and the contrast is quite interesting, so I thought I'd take some photos and upload them as a general guideline.
A carnivorous Mexican Pinguicula... This is photo I took today of a Pinguicula 'Tina', a hardy hybrid that is great for beginners. The plant in this photo is in its carnivorous state and is readily producing large, sticky leaves for catching and digesting insects. Note the pale green colour. When the light strikes the leaves of a Mexican Pinguicula that is producing healthy carnivorous leaves, you may notice that the light itself permeates the leaves reasonably well and, in some cases, can even make them appear as though they are glowing. This is a healthy plant.
A succulent Mexican Pinguicula... Here is the same plant as above, but last winter. It is in its succulent state and has been for a while, made particularly evident by its smaller leaves which stack on top of each other in a tight rosette. Note the change in the colour of the leaves: they are now dark green and the mucus producing hairs are somewhat noticeable. Light would not permeate these leaves very well at all. There are also dried, dead leaves around the edge of the plant, but these are not in excessive quantities and are a common by-product of entering the succulent state. This plant is healthy and came out of its succulent state the following spring and produced two large, beautiful divisions. This plant received very rare watering over the winter.
A dehydrated Mexican Pinguicula... This is one of the aforementioned divisions. It's planted in an awkward-to-water container, which is why it's in the state it's in. The leaves are very similar to that of a succulent Mexican Pinguicula however you'll notice not only how darkly coloured the leaves are but also how dull they've become; the centre-most leaves are starting to take on a rusty colour and the mucus producing hairs are very noticeable. There are also elongated, dried, dead leaves around the outermost edges. The leaves on the underside of the plant are elongated, too and, while it may not be evident from the photos, this plant is noticeably smaller than the others. This plant is being kept in the same growing medium and conditions as the one in the first photo, with the exception of the level of water its receiving (which I aim to rectify).
List of online carnivorous plant suppliers