alright, i tested the particle settings for water and as i already wrote in my very first post, those are limited to newly started games. you can't just mod them and load a save in the later game, which is a shame. anyway, here are two screenshots:
normal particle settings:
particle count for all particle settings raised by factor of 10:
update: half the particle count for each particle flag
there is little, or even no difference between both pics. it looks like the particle count is capped. in fact, the framerate showed no impact by the values, even though i restarted the game after using them. i assume that the values are capped at 32768, which might be still too low to see no difference to 20,000. using like 300 or 400 made it look like a mix of turned off advanced physics and with the same feature enabled, showing the normal thin water streams with only very few of the "big" water bubbles coming through the door. i guess i'll experiment with other values now. may be lowering the count to 10,000 or even 5,000 would already be enough for no visible difference