Would it be safe to use a 400 watt hps this close to a water heater, would heat affect the water heater at all it says no flammable vapors or liquids bc of the gas and flame.
You should be pretty safe to grow around your water heater. From the look of the picture it appears electric and not gas. A gas water heater might not be the best thing for your plant because of how gas water heater room needs to be set up. The picture shows that it's ventilated through the top and you'll want to make sure that the seal around it is not broken or loose like some old ones are. If it is loose or broken you could be emitting some harmful shit into your air which would be bad for you and the plant. In the end you should have no problem. I would recommend having a very study set up for the plant and the light system so no accidents occur near the water heater. Also just as a precaution you could buy a cheap carbon dioxide alarm (just like smoke alarm) if you're worried about the plant in that sense. Hopefully this helps you out. I recently replaced my gas water heater and installed an electric myself and that's where I'm getting my information from. Anymore questions just let me know. I have a lot of experience in being a green thumb also if you know what I mean!
I hope you have more experience in being a green thumb than a plumber, because electric water heaters dont have exhaust vents. Electric heaters have heating elements they dont burn gasses so exhaust is not needed with electric. If you just installed an electric one yourself take a look at it ( no exhaust vent).
Please do a little research before you try to dismantle someone's answer to a question. In your reply you said something about exhaust vents which I don't believe was mentioned in my answer. What I said was that his water heater appeared to be ventilated through the top. There are electric water heaters that are vented through the top. You can look it up online and better educate yourself if you'd like. This website was not created for people to go around searching to try and find something to make fun of someone about. Grasscity is here to help people as I was trying to help the original poster. If you don't want to contribute in a positive manner then you might as well not log in.
There is no reason, gas or Electric, that you can't set up anything you want in that room as close to it as you want. You'll be fine, Now if you need to know why its cuz... 1) Nothing in your light will be able to ignite your pilot light or the leaking gas, should it go out. 2) Nothing in your light is ignitable, should it com in contact with the pilot light on your heater. Its all simple common sense even if your as blazed as me.
Falling lights are always a hazard though. Even with a sound set up there's always chances one could fall and catch flame to something. I've definitely had a few plants toasted this way. If there was a faulty gas heater then this might not be the best idea. To the original question though, you'll be fine with that set up.
I say go for it, just keep an eye on things if your worried. Im currently growing next to my fuse box.