V40 2018 not starting - water in starter moter?

[BlueBells]

We bought a second hand V40 3 months ago. Drove fine up until 3 weeks ago where it wouldn't start.

The garage said they found a large amount of water in the starter motor, and put in a new one. They told us the only possible way this could have happened is if we had driven through a flood.

Here's the issue. We have never driven through a flood, or even a deep puddle. We live in London and don't drive it often, the last occasion before the episode was a sunny day. The mechanics didn't believe us.

The car has remained on the driveway for a week since it came back from the mechanics. Today we went to start it but again it won't start.

The car is under warranty so we have to take it back to the same garage. I suspect there is water in the starter motor again. We again drove it on a sunny day, but there has been a huge amount of rain since it has sat on the drive. But the garage has told us that it's impossible for this to be caused by any other kind of water damage other than driving though water. Can anyone confirm how else water could have gotten into the starter motor? I don't want to take the car in again, not have the cause resolved, and just have an argument over whether we drove it appropriately.