What picture?

If TNT is in water, will it hurt me or mobs? Cause all I know is that it doesn't do damage to any block around it, but I have no idea if it affects mobs or the player.

It doesn't do damage in water... I think.

This.

Hell yeah, now all I have to do is figure out how to set the redstone on, thanks

Well if you're making a drop trap, it's pretty simple.

What're you looking to put into it?

I'm making a hole containing some water sources on the edges so all water flow comes to the center. It will capture a number of mobs, when 1 or 2 are in the middle (stuck), I pull a lever letting TNT pop up from the middle, then boom.

Why not just set the water on top of the TNT and have a lever activate the TNT down at the bottom.

I want to make it more complicated, don't ask me why, seriously :3 I just want to challenge myself.

Ok, this'll take a bit to reset, but I think it's fun.

Make a basic door trap, except put the pressure place on a block of sand.
Have that block of sand be held up by a torch.
Off to the side, have a piston holding back the flow of water.
Flip switch, piston retracts, water takes out torch, mob falls.
From there, since the water creates a slow flow down (unless you quickly flip switch, making it a drop kill) you can set up a TNT trap at the bottom. Or both if you're feeling particularly killy that day.

Or - Leave the water flow to drown them, and collect loot.

Note: Can also have the mob fall onto another pressure plate that sets off TNT.