Yes, you can. But there are TWO things that you need to do:
1 - protect it from frost
2 - protect it from direct sunlight.
1 - protect it from frost. Simple - run it when it's frosty. The temp of the mains water is always well above freezing, so it warms up the unit and prevents freezing.
2 - make a wooden or fabric cover to shield it completely from the sunlight or you'll get green algae growing in it. I speak from experience!