Since your temps are moderate, and you do get sun...
I would recommend either using a solar powered setup.
Or... get free fogged windows from a window place... and use those to make a greenhouse type area around where the water sits.
The solar greenhouse setup will warm it up nicely.
If...
How cold do you get?
Do you get any sun?
I find it way easier to just bring out fresh water every morning.
Some people in warmer places find that if they bring the water bowl/whatever in every evening, and then out every morning... then things work well.
Night time temperatures are just...