The qualifying competition saw four teams contest three vacancies in 2017/18 alongside Bedford, Warwick, Caledonia Storm, Leeds and Sheffield Dolphins.
Coventry, who last played National League men's water polo seven years ago - and spent four seasons in the top division before that - had little difficult securing their place, winning all three matches.
It was far less straightforward for Chelmsford, a club that last took part in the men's National League 17 years ago. Much depended on their final match against Spalding, who were seeking to retain their BWPL membership after finishing in the bottom three in Division 5 last season.
Victory went to Chelmsford - 8-5 - and so Spalding drop out. The third place went to Watford Saxons, whose only defeat was against Coventry - 10-5. See Results page for more details.