Let me share my experience with water while doing journey. why sharing with you this bad situation one day I was doing journey from bangalore to chennai.
But I took some food stuff and one water bottle at that day I had food and water after that night I got omit because that water bottle not isi mark water and also they might be filled some other waters.
I mean not filtered water but this is very dangerous if you are purchasing water bottle before that dont forget to check the seal of the bottle and as well manufacturing date but usually while I am doing journey I will prefer only bisleri company water bottle.
I will purchase it outside only because in train so many sales person will sell ordinary brand water those are not filtered water so please take good water while doing journey for health consciousness I will prefer only bisleri water is good. and especially its indian brand as well.