[thedetailguy]

I googled how to clean water spots off of vehicles and I read that hydroflouroric and hydrochloric acids mixed will do the job. I need expert advice on this. What the mixture should be, precautions to take, and how long can it sit on glass and the body of a vehicle.

[XeLa.]

I would strongly recommend just using a dilute white vinegar solution in its stead, as hydrofluoric acid is hard to come by and for good reason - it's highly corrosive and it's a strong contact poison (damages internal tissue upon contact with the skin.) A solution of dilute white vinegar applied lightly to the appropriate areas (firstly washed so that you don't grind any dirt into the paint) should do the trick, as the water spots are just the build up of calcium and magnesium deposits from hard water (dissolvable by a weak acid like vinegar.)

N.b: Just make sure to do your research beforehand, there is plenty of reliable and not so reliable information out there.

[Arkcon]

I googled how to clean water spots off of vehicles

I'm glad you've done some research.  Lets work with that.

and I read that hydroflouroric and hydrochloric acids mixed will do the job.

I'd like to see exactly where this information came from.  This is the beginning of a bad idea.

I need expert advice on this.

Yes you do.

What the mixture should be,

What did your reference say?

precautions to take,

There are several, but I'd start with not doing this. 

and how long can it sit on glass and the body of a vehicle.

The chemicals used to make clear coat are quite resistant when new, but they do change with time and end up failing to resist the acid.  So its hard to give a definitive answer.  Diluted HCl could damage the finish instantly.   Or maybe bead off a new clear coat or waxed car, so it might work.  Or be a disaster.  That's the thing, it could work once, on a tiny spot, and be destructive and dangerous afterward.

Or hurt people.

Hydrofluoric acid is pretty dangerous for a layman to use, its not something to spread across an entire vehicle.

I'm given to understand, the "Tire Shine" products are very dilute hydrofluoric acid.  I also know that they're supplied as concentrates, which puts the people mixing them at risk.  Just a bad idea all around.  Also, hydrofluoric acid's ability to dissolve silicates means it will rapidly ruin glass.

[Babcock_Hall]

As a very amateur car detailer, I have generally liked this company's products.  Meguiar's hard water spot remover includes ethoxylated alcohols and citric acid as components of this product.  They don't provide all that much detail, but that sounds much, much safer than working with hydrofluoric acid.
http://www.meguiars.com/content/en/msds/M47%20SDS.pdf

[Grant Hanley]

Wash your car and then wipe it down with a chamois soaked in distlilled water, or rain water from tank. This will remove the water spots as pure water doesn't contain calcium, which causes the spots.