[Trillium]

Rainwater is absolutely the best for blueberries as they're such acidic loving plants that most tap water (alkaline) over time will increase their alkalinity. So get those water butts saving while you can. And yes, a lot of blueberries do like boggy conditions, which is their natural habitat, along with cooler weather and conditions.

Check out this video
 http://www.gardenersworld.com/how-to/projects/blueberries-cranberries-growing/