Fallout 4 Survival Tip - Fill empty bottles with Purified Water at water pumps and working sinks - YouTube
Fallout 4 Contraptions DLC - Water Collection System - YouTube
Posting because someone asked about this. Purified water farming at sanctuary. You can go way past 999 water but you have to look in your pip boy (workshops tab) to see it.
Survival Skills: 10 Ways to Purify Water | Outdoor Life
Purified water (Fallout 4) - The Vault Fallout Wiki - Everything you need to know about Fallout 76, Fallout 4, New Vegas and more!