It's probably a blessing in disguise. That's way to long for fresh water to sit. The dilution is a good thing...after you get the issue resolved. Keep fresh water fresh...you never know when you will have to call on it, as in CG water system failure, breakdown on the road or Armageddon. The check valve as mentioned isn't difficult to fix.
2018 THOR Chateau 35SF
Two Labs, Bugsie & Blondie