Place a light source nearby
Cover the water with a block or roof
Use slabs, stairs, or glass blocks above the water
Keep the area in a warm biome
Place water indoors
Use a campfire, torch, lantern, or glowstone near the water
Prevent direct exposure to the sky
Use flowing water instead of still water where possible
Move the water below Y-levels where freezing is less of an issue
Replace exposed water with ice-resistant designs like bubble columns or cauldrons