Hello All,
Need some expert advice on how to fix water ingress problem. I have a big water tank on to the side of the house and next to it a shed with roof inclined towards the tank. As shown.

When it rains the water is seeping in and created gap between the external wall and the concrete slab.


I was thinking of removing the tank, fill the gap created. Removing tank is a bit labor intensive I believe.
Any other ideas please.