Need help - potential water issue
Our house is a little over a yr old and today I noticed the inside wood window sill appears to be buckling and has a water stain (in the left corner only). We never use this window so it has never been left open to allowed rain in. Any idea what could cause this? When I open the window there is not standing water inside the sill. Attached is a picture; any advice or feedback on what to do next or potential causes is appreciated.