The U-17 trophy was shared between both sides, as per the tournament rules with Waterpark declared the winners on try countback.
By bringing the cups back to Ballinakill, the Waterpark youngsters emulated their club colleagues of three years ago when the Park Under-16s and Under-18s were the first to do the league final double.
In the Under-17 final, Garryowen winger Patrick Healy got over for a second minute try before Waterpark replied when scrum half Conor Hearne picked from the base of a ruck and scooted through a gap, with his half-back partner Tom Kiersey adding the conversion.
But the Light Blues, despite coming under some pressure before half-time, built an 11-7 lead for the break with out-half Mark McGrath converting two well-struck penalties.
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