The best way 3 rbs burst with 1 non rb is if the 3rbs are all fire and one of them is mage with wit JS spell. You didn't give any information about your team so it's kinda hard advice on how to exactly burst your water. If your water doesn't have GS tho and u have 3 rbs why not just get him GS spell? It's not that hard and will be worth it in the long run for more exp for your character.