The pure water produced as a result from one of the recipes in the nitrogen chain can't easily be removed. It can be put into an electrolyzer to vent hydrogen/oxygen, but that seems a bit of a hassle just to get rid of water.
I've made a quick recipe mod which adds pure water to the gas venting pump to circumvent this issue.
I'm well aware that venting fluids isn't the intended purpose of the gas venting pump, but this seemed to be an easy way to implement it without having to add a new vent entity.

Could you consider adding this fluid to some kind of void/vent mechanism? It could probably even pollute a little bit as an offset, as distilled water can leach minerals due to concentration differences, potentially depleting mineral contents of soil faster. (or similarly, use it to remove pollutants from the game world?)

From what I recall, there are 3 recipe chains that produce pure water as a byproduct.
The first is in the Hydrazine chain, however, this is far less than the requirement of pure water to begin with, and with the use of overflow/underflow valves (or if you don't have the logistics mod installed, pumps wired to the tank with some logic), you can prioritise the byproduct water feeding into the electrolysers first.
The second is on the RTG chain. I think this one is perfectly balanced so it produces exactly the amount you need, so you can feed the output back to the input, and it's self sufficient. You just need to add a little to kickstart the process.
The third one is from the Deuterium process, Water is split into mostly pure water, and a small amount of heavy water. This one is intentionally a pain in the arse because if it were easy to just get rid of the pure water, you'd basically just end up with a lot of high end fusion fuel for very little effort.