water Spraying plants with water?

I was reading through a gardening book that I found on my shelf and it had this tip for peppers.

Is there any truth to this?

     I don't know if it will help fruit set but it will definitely make bacteria happy.

Chile plants don't really need a lot of help in making fruit "set", as they are self-pollinators. If you are growing indoors, once the plants begin to bloom, you can a) give the pots a good thumping - enough to shake the plant, b) run a fan on them (ideally, oscillating), andor c) just run your hands through the foliage every day. A fan is a good idea for another reason: it helps prevent the top-of-soil fungus (known as "damping off") from occurring. Damping off can kill your plants. Plus, the breeze from the fan will ensure pollen gets moved. 
 
Regarding spraying with water, lots of folks will tell you to just spray off mites and such. That only temporarily helps. If you get mites, better to use an insecticidal soap or, in cases of infestation, a miticide.

Eek yea I dunnno I would do that. Especially in a greenhouse. The humidity is already pretty high in a greenhouse and spraying it with water might cause some mold issues among other things.

It probably just slightly shakes the plant, which led the author(s) to believe that it was the water helping set instead of the force on the plant doing it. And I wouldn't just spray around and expect it to take care of mites. Maybe shooting them with a stream of water, but I wouldn't do it regularly.