Q: We took carpeting up from our bedroom which has hardwood floors underneath. When cleaning the carpet from pet urine there are severe dark watermarks. Is there a way to lighten the marks before sanding and refinishing?
A: The water marks are likely urine also. Your best bet is to replace the affected boards prior to sanding and finishing.
(Fyi – Lots of experiments to read up on re: urine stains in our Q&A!)