Misting Plants with Brackish Water

Not advisable unless you don't mind getting salt deposits everywhere as the water evaporates.

What are you misting? People or plants?

These questions are so, so incomplete as to be useless to all.

I am misting plants

Why would you want to mist your plants with swamp water?

You're trying to kill the plants then??

Concentrated salt and mineral deposits will not be good for most plants.

Brackish really isn't enough to go on, but:

You'll need to filter for a couple of things - sediment/organic trash otherwise you'll clog nozzles.

Chemicals - Arizona Misting Systems has available a calcium filter that prevents hard water clogging of nozzles with mineral deposits. But they are strictly for hard water.

But - why would you mist when a plant really likes a drip system? Most don't much like the leaves wetted other than infrequently.

is it possible

yes, for a while.

why do you want to use brackish water? Your plants won't like it, and your misting system will rapidly get clogged by salt and mineral deposits accumulating at the nozzles If you're trying to make use of an existing water supply you should be able to do so but you'll probably have to spend money on filtration or be plagued with problems including a garden of dead plants...