I would think that the photo was taken to document the growth of the hollyhock in the dirt, so the water butt is an added bonus. The cottage stood end on to the road so that the front and the garden were south facing, so this hollyhock is enjoying the morning sun against this wall. This would have been in the 1940s at a time when the mains water was not connected and a well in the garden was the source of water for the cottage, along with water butts, there would have been one at the top end of the cottage and probably more near the chicken shed. Although rural, it is not that rural (being only about 10 miles south of the suburbs of Birmingham) and I think it wasn't until the 1950s that they got connected to the main water supply. The other day I was reading a local newspaper from 1912 and it mentioned in there that connecting the village to the water mains was under discussion, obviously it took a while longer to get the lanes connected.