Start with what you can see and smell. Yellow or brown ceiling marks, bubbling paint, swollen baseboards, loose flooring and a persistent musty odor are common warnings. A stain that feels dry today may still reveal a leak that appears only during wind-driven rain.
Inspect around windows and doors after a storm. Look for damp corners, separated caulk, soft trim and paint that blisters from beneath. Outside, check the head flashing and the joints where siding meets the opening.
Check under sinks, behind toilets and around tubs. Slow plumbing leaks often darken cabinet floors, soften subflooring or create mineral deposits before water becomes visible in the room below.
Walk the exterior and look up. Missing shingles, damaged roof penetrations, overflowing gutters, open soffit joints and cracks around additions can all direct water into concealed framing. Also make sure soil and paved areas drain away from the house.
Do not rely on paint to solve the symptom. Water damage requires two repairs: stopping the source and replacing material that can no longer perform. If you find softness, recurring stains or mold-like growth, have the full assembly evaluated before closing it back up.