Have beer down, but apparently not sparkling water

We've been homebrewing for about 5 years now, and switched to kegging a year or two ago. We've made a wide variety of beers, and ciders too, but apparently we can't manage to keg water successfully. It's getting old.

I just want to have sparkling water on tap. But we've tried it a few times, and every time it tastes really, really metallic when we force carbonate it in the keg. We don't have hard water, our water tastes fine normally, and we filter just in case. None of our beers or ciders have tasted metallic in the least (I've got sensitive taste buds, I'd notice).

We've tried airing it out overnight, making sure that there's no normal air in the keg, and replacing some of the fittings.

Is it possible our water is too soft, and it's leeching metal out of the keg/fittings? I'm out of ideas, and haven't a clue how to solve this problem.



Help!

My other half loves her seltzer water. 2 of my 5 kegs, and my 20# CO2 bottle are permanently reserved for her seltzer water. I keep two kegs in rotation, so one of the two are ready for her at all times.

2 things to consider.

She has told me before that there is "a taste" right after I clean & sanitize them. I don't clean them any more, though. Once she empties one, it's opened, filled, and put back under pressure immediately to carb up while she drinks the other.

Try adjusting how much CO2 you put into the water. We keep ours at 30 pounds. She complains of "weird taste" if I try to conserve and run her seltzer water at 20 pounds or so.