They don't need warm water. What they do need is enough water to swim in. Make sure they can rest on some rock or plants to prevent drowning. My setup can be seen in my picture gallery. The bottom of my setup is all water, and I have made a couple of hiding spots (they like to hide from time to time) and also enough room to walk about and eat. I also have a waterfall in my setup to keep the water moving. I also change 1/3 of the water every week. Maybe your toad is holding it's winter rest. They don't move and eat as much as they do normally. What's the size and setup of your tank?