I'm bothered by all the overwhelming quantity of talk about extracting hydrogen by splitting water. If you're talking about wastewater treatment type water, I wouldn't have nearly the problem with it as I have with people using already scarce groundwater resources. You do NOT have to do that to get hydrogen.
You already generate hydrogen yourself. What you flush down into the sewer and toss into the local landfill generates hydrogen. You should be using that hydrogen instead--and it is passively extractable, no electrolysis involved whatsoever.
You do not generate pure hydrogen yourself--no. But all you have to do is pass your gas through a silver (reusable) filament filter or an iron (not reusable) filament filter and out will come pure hydrogen. If you use an iron filter, then you can generate both pure hydrogen and as a byproduct make blueberry fertilizer.
Waaaaaaaaa.....??????
I'm talking about your natural hydrogen sulfide. It's a simple compound of hydrogen plus sulfur. As the silver filter tarnishes, you don't have sulfur attatched to the hydrogen anymore. As the iron turns into iron sulfide, you don't have sulfur attatched to the hydrogen anymore either.
And yes--iron sulfide is a blueberry fertilizer, good also for azaleas.
Got problems with tree roots in your sewer line? Use a copper filter instead. The byproduct is cupric sulfate which, when you toss a bunch of it down your terlet, flush once, let sit for 8 hours, will kill your tree roots in a manner approved of by your city waste water people. Cupric sulfate is sold over the counter expressly for the purpose of clearing your sewerline of tree roots.
How 'bout THEM apples.