I would pick them up and see how heavy they are. If they're fairly light I'd water, if heavy, they're fine. You do have a plastic covering of some sort over them to keep the moisture in, do you? If they are drying out at this time of year, you possibly have too much ventilation in the covering for them. I've only been w/s for 3 years and I'm pretty sure that I haven't had to water until it was actually spring and the seedlings were starting to come up already.

Hope this helps,
Laurie

And was the soil moist when you sowed your seeds? If it wasn't, you should water them. I do mine by sitting them in a tray of water and letting it wick up into them. But at this time of year, your soil should be pretty frozen. How about condensation? Most of mine are covered in snow, but the ones on the deck get condensation in them during the day, which indicates that they're moist enough.

As Laurie says, most years you don't have to water until later in the spring.