LMSC The tea from mineralised RO is lighter and taste a lot better. I always found the tea with hard water even with a drop of milk was harsher in taste.
My wife far, far prefers the tea made from the service boiler, which is zero water and sodium bicarbonate than from the kettle. Not only does it taste a lot better, but it even looks so much better too.
I live in London and the tap water is pretty horrendous, so maybe not such a surprise