Planet Minecraft

I've been playing Skyblock recently and I wanted to create a mob tower. The mobtower requires flowing water, however because it is in a snow biome, the water will freeze and defeating the purpose of a mobtower. In addition, I could add torchs to the water, making it not being able to freeze, however the light will block the spawning of monsters. Unless their is another mobtower design that uses the given blocks in skyblock, it seems impossible.
If anyone has any idea WITHOUT SWITCHING THE BIOME (unless that's the only choice), please include below.