I know that I am super late and if this does ever get added it would probably be next summer, but what my idea is would basically be a snowball cannon but it shoots Waterbombs here is what the stats would look like (I am no good with actual gun stats but ill try my best)
Name: Waterball Cannon
Price: $19999 (to be similar to the other waterguns ending in 999)
Damage: 3-5, just dont make it op
Freeze: Same as snowball cannon
Rate of Fire: Same as snowball cannon xD
Auto: No
Event Blocked: Yes
(If i missed any specific stats tell me and i will add)