The choice between a pure and hybrid Water/Electricity Sheep really depends on your defence. A Water/Electricity Soul Master can be very good if you balance your MA, LK and HP.
Besides the blessings, you'll also have access to Undine's Garden for decreasing monsters' electricity resistance. Staff of Thunder is a pretty nice skill and Aqua Bomb does above-average damage for a single target spell. All in all, it's not bad, but I still prefer Fire over Water.