Just that, where can I get heavy water from?

How I can make Hydrogen Sulfide? Because I can't seem to find recipe for it?
Ok, figured it out: seems like I have recipe for Hydrogen Sulfide (well, it is "Siarkowodów (gaz)"), but it has icon of 3 atoms over flame-like icon with biggest part being yellow and two lesser flames being white, and to make Heavy water you need Hydrogen Sulfide which is only icon with atoms...

true, I saw it, thanks

Water + Hydrogen Sulfide in a chemical plant -> 99.5% pure water, 0.5% heavy water.
0.5% sounds harsh, but consider that you'll probably already be using pure water for Electrolysis, and uranium has a 0.07% chance for U-235, and real world values would put it more around 0.02%, and it's actually pretty generous.

Hydrogen sulfide comes either from an alternate lead oxide recipe(lead processing research), or simply a new hydrogen + sulfur recipe.(Sulfur processing research)