ᐅ Basement window wet / water is leaking in underneath the window sill

Hello everyone,

We are currently still in the construction phase and have occasionally noticed that water has entered below the window sill of two basement windows. In some cases, there was so much water that it ran down the wall to the floor, or at least it was visibly wet directly beneath the window sill. The window well and windows are not designed to be watertight against pressure water.

We have not been able to identify the exact cause yet, but we suspect that water collects in the light well during rain, cannot drain away quickly enough, and therefore flows into the basement room at the window level. It is possible that water also enters the light well from the side...

We have addressed this issue with the construction supervisor several times, and he only said it would be resolved before handover. As a first step, the drainage of the light well was cleaned because it was apparently clogged with construction debris. Additionally, a glass pane will now be installed over the light wells to keep rainwater out from above. The groundwater stands about 30cm (12 inches) high near the basement.

The question is, of course, whether this is an appropriate solution or just treating the symptom? To simulate the situation, we plan to pour 1–2 buckets of water into the light well to see how quickly or slowly it drains away...

How much water should the light well be able to drain and within what time frame? Is the idea of installing a glass pane a proper solution?

Would it make sense to install a backflow valve in the light well, which would also filter debris?

Pictures 1 and 2 show the water flow quite well, picture 3 shows the well from the outside.

Thanks in advance for your feedback!