We have four foster kittens who are nearly five months old and over the last few days I have noticed wee in the drinking bowl. I have changed the bowl for a different type, taken away the plastic mat underneath, moved the bowl to another place but it still happened. The first time was overnight and I thought perhaps there was a problem with the trays being too used but it has happened since with virtually unused trays. It is only in the bowl and not elsewhere. Any ideas ?