Hi, dude!
The easiest way to get a water filtration units chematic:
First of all you need to finish all starting quests.
Next start "Creating a Journal" and "Gathering Information" quests.
After you hang up the map, you'll receive 4 Journal Chapters, Carboard Box scheme and something else.
Next, start "Advanced Survival Chapter".
After you'll craft a survival campfire and take a knowledgepoint, you'll get a water filtration unit schematic.
For knowledgepoint you can scrap Carboard Box scheme, because it's useless.
What do you mean?