Never heard that. But I don’t think any thing can be done to water. The only thing i can see, if you are using tap water:
– warm a little the water which can be cold out of the tap, some say it is better to avoid cold water on your plants.
– The chlorine tend to go away if you heat the water, and is not always good for your plant

I thought ice on plant roots was supposed to stimulate growth?

I don’t know, when I take care of plants, they die… I have never been fond of plant biology either, and could never have been happier than the day in a plant lab my instructor told me that she would never want me near her research lab.

But I have the feeling than in gardening as weel as in cooking there are a lot of untetsted recipe/tricks that are transmitted by word of mouth and I don’t know wether they work or not. I was just trying to find a logical explanation for the reason one would want to expose water to the sun before using it to water the plants.