I use to buy the same water didn't know anything about fish back then.Actually, my first fish was a goldfish. I was about 4 when I won them.
My sister won one and I won one at a church field day .We had them in a little 3 gallon terrarium, with no filter.
We used distilled water for water changes. (My mom did all the work, but she did daily 100% water changes)
One day she used tap water instead of distilled water, killing the fish while we were at school.
Still beat myself up about it, knowing I could have done better.