Beery tasting soda water

I’ve been using my kegerator to make carbonated water so my wife will stop spending $1/liter on the bottles at the grocery store. The problem is there is a funny twangy taste to the water, and I can’t help but think I’m smelling and tasting the gas from some of the kegs hooked up to the same CO2 tank. A system diagram is shown below. I do have the ball check valves at every connection similar to NB item#K125.

Last year I tried making a whole keg of carbonated water, and it was fine initially but after 3 weeks tasted strongly of beer. I have since discovered one of the check valves was a cheap plastic cone instead of a ball, so I replaced it but have yet to try the full keg again.

Recently I’ve been using the carbonator cap on individual bottles and they still have that subtle acidic twang that I don’t get in the store bought water. Could this just be the residual beer in the gas line between the QD and the check valve? Is anybody else having this problem or can you suggest something to try?

The K125’s are represented by the little purple squares, and the orange squares are 1/4" FPT air tool splitters from harbor freight. The low pressure regulator does pass 30 psi to one line through its high pressure port.
[attachment=0]CO2 diagram.png[/attachment]

I hook my carbonator cap directly to a regulator which is stand alone and do not have any taste issues. Can you run a test and isolate the carbonator cap to a regulator which is not part of your beer system to see if it cures your problem.

I’ll try that, I’ve got a regulator I use for the portable system that doesn’t normally sit with beer hooked up.

I was thinking about this a little more yesterday. I often hook up the gas through one of the beverage posts to carb faster and several times have seen beer enter the check-valved line after sitting for several days. I can see a little bit of beer backup if the pressure from check valve to line is less than keg pressure + liquid column pressure. However, it has always made me wonder if the check valves are working properly. I’ll also see beer run into the check-valved line if it’s hooked up to an overcarbed keg.

If I shut off the tank and purge all the line pressure, should all the check-valved lines keep a small amount of pressure (valve to QD) if they are working properly?

I would expect that that would be the case.
I had a similar set up to yours, less the check valves, and after getting frustrated with several issues I finally bit the bullet and changed over to a system with a separate regulator for each keg. All the Issues were gone and it’s nice to have the ability to control each kegs pressure individually.