I once saw a yellow wagtail land in my back garden in London. The nearest water was a mile away. That's unusual I think.
Going by what I've read, they do tend to favour damp areas like river valleys, marshes and wet meadows.
On the other hand, the Grey Wagtail can, at times, even be seen in city centres. Just reading up on the Grey, it says they take midges and suchlike over water. That ties in with the Greys I've seen around Sefton Park lake. Lots of insects hovering around and above water there.
Lovely little birds they are too. 🐤