Re: head gasket
I've never had a blown head gasket, but had problems with the heads "lifting" which is something different (it causes the cooling system to over pressurise and blow out the overflow)
Water out of the tail pipe isn't something i would usually be concerned about, unless it is happening after the car has been driven for a good long drive, which gives the condensation in the exhaust time to dry out.
I presume that the engine is otherwise running ok, its just losing water. I've never seen water out of the exhaust caused by a blown HG, unless its fully blown, in which case the car would be undrivable. That's not to say it cant happen, its just that ive never seen it before. Even if a ported exhaust port had a pinhole in it, i doubt there would be enough volume of coolant for it to make it out of the exhaust in liquid form.
Are you at full operating temperature (including the exhaust) when the water thing happens?
If you are still concerned, try some bars leaks and see if it improves. Have a radiator pressure test done.