WvW Water Ele Assistance
Definitely take arcane if you want to be supportive, both EAs help.
Then obviously take water, as I assume you are, and then probably fire because earth and air tend to be less team-oriented especially in zergs.
In terms of playstyle, even if you want to be as supportive as possible you’ll need to swap attunements constantly, even to fire which in your case is still solid damage with an evade and a constant fire field.
So first and foremost, a little bit of a disclaimer I guess: Generally speaking, the best way to help your team out is through traiting water/arcane skills but taking DPS gears and runes. No matter what healing power you have, all of the healing skills on the staff are too slow to be of any real effect as heal skills on their own. Instead, you use the water fields to blast for a huge AoE burst. Guardians are better suited to this than an Ele, and since the blasts will scale of whoever blasts its healing power, stacking on Healing is pretty useless for a backline ele. To be the most useful, consider looking into a rune set like strength and look into a mix of zerker gear with solider gear. Celestial isn’t really all that good for an Ele Staff in a zerg. It smuch better for D/D roaming. Not that it wouldn’t work, just there are better options.
On that regard, I’d recommend taking in water: 1-1-1 for more personal survivablity or 3-2-1 or 3-3-1 for more pure zerg support. With arcane, probably 2-2-1 or 2-3-1. Evasive arcane gives you an extra blast finisher for more AoE buffs and a nice AoE heal. Your last slot I’d recommend fire with 1-1-1 for group fury/might blasts or 1-1-2 for more DPS in general if you want to support your team.
That said, I know it can be pretty fun just trying to support the zerg through heals and regen. If you want to something like that, I’d recommend looking into Rune of the Monk (From AC) and picking up a Sigil of Benevolence. This will increase your healing quiet alot if that is something you want to see. Other good alternatives if you want to do a pure pure support build include Runes of Altruism, which will grant stacks of fury and might when you use your heal skill to others around you. I know that when I ran a full healing build with monk runes/rice ball/benevolence, my heals on the staff were popping up at nearly 3-4k a tic with geyser, nearly 2k on water blast and my evasive arcane dodge. The problem with it is getting people to stay still for the full duration.
I hope this helps in some way to atleast give you an idea of how to progress