Tap water other than in in soft water areas should not be used on Blueberries due to its alkalinity. However if you added some Lemon juice or vinegar to the water to neutralise the alkaline content wouldn't it then be OK to use on the Blueberries?
Tap water is treated Invicta. I wouldn't use it even in soft water areas.
But wouldn't the added acid neutralise the chlorine in the water?
Adding acid can lower the pH but it will not soften the water.
Hard water is due to dissolved calcium and magnesium in the water.
Have you got access to rain water? I have a small water butt attached to our shed that I use for mine.