I can't use my own power directly, or the demons will just absorb it, and a lot of it is blocked by the cursed shackles anyway... but what little I have, I can give to them. It might give them a jolt.

[At the very least, it will solidify their physical form enough for interaction of some kind.]

I don't think touching the water is prudent, so sending a talisman is probably the easiest way.