Legal Question in Landlord & Tenant Law in Missouri

It is unclear what valve you mean, or how it was broken. Generally, plumbing issues inside the building are the responsibility of landlords, especially when it is a multi-unit building. However, many lease agreements include a clause whereby a renter is responsible for repair of items that are broken due to misuse or vandalism by the renter/occupant or their guest.

You did not indicate HOW OR BY WHOM you were billed, but you did seem to indicate that the bill you are concerned about is regarding the water bill, and may not include the cost to repair the broken valve. In light of the description above, you are just as liable for your use of water as you were before. If the water company was billing you, and not the landlord, you may remain liable to them for the bill. If the "valve" was outside the property owner's portion of the service line, the water company may have to eat the additional bill. If it was within the property owner's portion of the service line, then between you and the water company, you remain liable.

If water was included with your rent payment, the issue is tougher, but may be clearer. If the damage to the valve (no matter where it is) was not due to vandalism, neglect, or misuse, you should not be liable for the additional water bill that can be attributed to the broken valve. That is the easy and clear part. The tough part is determining (such that it could be proved in court) that the damage was not from vandalism, neglect or misuse. Once you've done that, the toughest part is proving what portion of the extra water bill is attributed to the broken valve.

Good luck