They're wrist mounted. "Martin uses his power to freeze the water as he fires it. Like an ice gun."

She gets one. "That sounds mean."

"Eh, super kids play rough I guess. And I think he wants to use them to fight baddies...like you!" Squirt!

"Ack! You found my one weakness! But I will stop you, beast!" Squirt squirt!

Perhaps unsupringly, the water does not deter the son of a mermaid.

Oh no! What if she sprays him on the face?

That's a little more effective, but also, Mer reflexes!

Augh!

...what if she cheats, though. She can fly.

Michael cannot. Why do you think he wants to Manifest?

Yep. So she can cheat with that and squirt at him!

He can grab at her ankles!

Eeep! Splash splash!

He manages to pull her to the ground and grins.

"Argh!"

"Ooh, let's try these in the time room!"

"Okay!"

Time seems to run really slow in there.

Well what does that actually mean in terms of observable consequences?

Michael's dancing is in slow motion.

...and if she steps inside?

He is dancing normally. 

"You looked really, really fast."

"You looked slow! Okay so I'm gonna go outside and I'm gonna give you a thumbs-up, then you count to five and give me a thumbs-up, okay?"

"Okay!"

So she goes outside, and then thumbs-up!

It takes quite a while for Michael to respond in kind. He appears to be raising his water gun.