Excellent answer from Ethel especially about the plastic bottles. All water (except distilled/deionised) has minerals dissolved in it. Hard water has more than soft.
If you don't like the taste of your tap water just add some diluting juice to it.
If you are going out for the day just fill up an old plastic bottle.
If you like a cold drink at home don't run the tap for ages and waste water. Just fill up a jug or old bottle and put it in the fridge the night before.
I'm not an eco-warrior but just trying to do a bit for the environment and not waste money.