Bit of a weird one but here goes. Over the last week or so whenever anyone uses the shower or flushes the toilet, clean water leaks out the bottom of the patio door, about half a cupful onto the sill. Bathroom upstairs, all waste water/soil pipes run down centre of house then out through front of house. Patio door is at back of house. Only pipes going to back of house is to overflow which comes out of wall just above patio door and is dry. Ground floor is bitumen on concrete and dry. No damp walls or ceilings. Toilet isn’t overflowing or dripping. All pipes under bath good. No issues when using water in kitchen. Is it possible water could be tracking from overflow into wall cavity and into patio door frame and if so, what’s causing it? Can’t work out where water is coming from. Help!