How to give water to baby

Hiya,

Baba is 6.5 months old and we drink bottle water at home as we are renting and water is hard so lots of limescsle on our taps etc

I’m boiling cold tap water for 5mins, washing a Pyrex jug and pouring the boiled water through a tea strainer into the washed Pyrex jug to cool, and then storing in a carafe with a lid. I’m then giving her the water in a Nanabebe breast - looking feeder.

Is this fine?? Because her poopie has become stringy and runny now :/

And when I boiled the water and let it cool down, there was this kind of film effect on the top of the water, in patches (which is why I’m straining it).

And how long can this boiled water be stored? And should it be stored in the fridge? And should I be using this water for washing her feeder, and dining plates and cutlery instead of the tap? (I’m in a rented property in the UK).

Thank you 🙏🏼