Window sills

[SJacks]

Hi, I wonder if someone can help before I embark on DIY. Our house is pebbledashed and has concrete windowsills. When it rains, huge streaks and water stains show under some windowsills. The windowsils dont have cracks. I have consulted tradespeople and they have no explanation and therefore no solution. Does anyone have an idea what might be the cause and how one can remedy this?
i attach a photo. the wall looks soaked, but thatvis after 48 hours of rain, sp please ignore that. Any advice gratefully received.

 

[DiyNutJob]

It just means the sill hasn't a drip edge, allowing water to move towards the wall.

 

[SJacks]

Hello and many thanks for your reply. The sills have drip eges, we had that checked. But

 

[DiyNutJob]

Either your drip edge isn't working or there are channels in the sill to let water get behind the drip edge.