That's what I've done....
I kept my ventilated 1000w at the same height that I'd had my open 600w
It's roasted the central growth.
I've never heard of a water cooling system for HID's....
Sounds potentially devastating.
It is called the Fresca Sol. Inner and outer class tube, the water path is about a 1/2 inch space between. Not that bad of price.
They even have a wide, 2 lamp, end to end type.
It was a wet bitch to set up. But, now it just works these last two years. I have my rig in a central hall bath and I took some wall board off and drilled down between the studs. I made sure I don't have any connectors, to leak under the house. Straight hose run about 30 feet, to a 100 gal garbage bin. In there is a 1/6 HP, sump pump hanging in the middle so it doesn't make any noise.
It is sits in a filter bucket and I run a little bit of Baqua (non-chlorine) spa stuff to preserve the water.
The key to the set up is not the plumbing, if you screw that up, it is very obvious.
The trick, it is to plumb in and wire a permission switch in the water flow. No flow no go. And i got very close to total lose of the entire rig one day, before I got that switch.
I was using a DIY float switch thing that failed. I caught it when the chamber was only 1/2 full, no flow, and the water was beginning to boil....2 minutes to BOOM.
Wheew....that was a close one.
I found one at Dwyers Instrument for $40. Saved $150 on that find.