Main plot of the game is about achieving rad free water, yet water just gives you about +1 radiation per second.

Credits to beelzebub1 & AlphaCentauriBear: without them I wouldn't have figured how the game fully calculates water radiation levels.

There are 5 types of water sources in the game:

• Purified
• Good
• Average
• Bad
• Terrible  
  

Each one has its unique heal and radiation values, the game then calculates with x2 multiplication variables how much radiation your character gets when swimming or standing on water,  based on which water type it is (e.g. Average Water Rad * Rad Mult Variable).

fWadeRadiationDamageMult - Multiplication variable of how much radiation player gets when standing on water.
fSwimRadiationDamageMult - Multiplication variable of how much radiation player gets when swimming.

This is probably in the wiki somewhere, but i like to do things on my own :)

Anyways, for some reason Bethesda set these variables to 0.1, which means in almost every single scenario you would only get +1 radiation per second when entering a body of water 🤦🏻.

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To make the game more challenging and immersive I've made the following changes:

fWadeRadiationDamageMult to 0.05
fSwimRadiationDamageMult to 0.5

Purified Water (Unchanged)
30 hp
0 rads

Good Water
10 hp
(+10hp with lead belly perk)
40 rads
Swim - 40*0.5=20
Wade - 40*0.05=2

Average Water
7 hp
(+7hp with lead belly perk)
60 rads
Swim - 60*0.5=30
Wade - 60*0.05=3

Bad Water
4 hp
(+4hp with lead belly perk)
80 rads
Swim - 80*0.5=40
Wade - 80*0.05=4

Terrible Water
1 hp
(+1hp with lead belly perk)
100 rads
Swim - 100*0.5=50
Wade - 100*0.05=5

Lead belly perk will halve radiation levels of these as usual.
Lead belly perk will also double hp received from irradiated water sources.

Additional change:
Dirty Water:
5 hp
(+5hp with lead belly perk)
(+2hp with sanitizer)
24 rads
(-12rads with lead belly perk)

Lead belly perk is much more useful now.

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Radiation resistance will affect these as normal.
(It was just my buggy save file that previously stop this from working)

Lead belly perk is much more useful now.

As always, you can edit these values with FO3Edit.

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My tweak collection:
FO3 GOTY CHEMS WEIGHTS
FO3 GOTY SKILLBOOK NO STATS
FO3 GOTY NO ANTI RPG PERKS
FO3 GOTY NO INTELLIGENCE SKILL
FO3 GOTY 5HP PER LEVEL
FO3 GOTY IMMERSIVE SWIM RADIATION
FO3 GOTY DEADLY RADS 60