I wonder if anyone can help please?

I've created documents containing a table in Word in portrait mode, and by necessity, with quite a full page - 0.5cm margin top & bottom.

Once I apply a watermark to the page the bottom cell of the table 'drops' to a newly inserted sheet, thus making a 3 page doc a 4 pager, and destroying the table appearance. This is irrespective of the font size of the watermark etc.

Any ideas please why this is occurring and how I can get around it?