Dank, occasionally you come up with an idea that bears closer examination. A houseboat might just be the perfect place to build the ultimate sealed room water cooled grow operation, and all you'd need is a waterpump! Put a debris filter at the inlet and pump cool lakewater all through your system to your heart's content- heck, you could even cool the living spaces in the boat with the same system! No AC required...
Only drawback would be to make sure you're drawing water that's cold enough to work. Warm summertime surface water at someplace like lake McConaughy or lake Powell is in the high 70s or even low 80s- perfect for waterskiing, tubing and the like, but it's too warm for chilling growrooms. However, in most lakes there is a thermoclime (a horizontal boundary layer) about 10-15 feet down or so. Below this level is a layer that can be as much as 20 degrees cooler. In many deeper lakes, you can get multiple thermoclines and if you draw from deep enough, say 60 feet or so, you can reach water in the 40s in the middle of the hottest part of summer! Keep in mind that there is no need for a pump powerful enough to pull water straight up 60 feet; it never has to pull from further than the waterline, which is never far in a houseboat.
While the hose is over the side you couldn't drive the boat anywhere but that's okay; just wait until 'lights out', haul up your 'anchor line', and motor around. Lots of people have houseboats, and some of them can be pretty big. A sealed room doesn't need to stink and can be kept quiet, especially when it's in night mode. Most boats always have some kind of pump or motor running, anyway. A big enough boat will have a tender of some kind, like a skiboat or runabout, which is the way lots of people commute to shore anyway. Yeah... this is starting to sound inspired...
Water? No problem. Cooling? Covered. Decent humidity? Check... Most houseboats have generators for power, so no eyebrows get raised when you need more go-sauce. So power is not an issue. For those with some creative juices, you could even build a greenhouse on deck, covered in translucent plastic to hide the nature of the garden from aerial inspection. Leave the sides of the boat intact so no one sees the greenhouse from waterlevel... to keep such tall sides of the boat from interfering with proper lighting, just turn the boat until the sun is shining straight into the greenhouse- a house can't turn to follow the sun across the sky, but a houseboat easily could!
Okay, any volunteers for a lil high seas adventure? Avast, ye lubbers! All hands on deck for the hoistin' o' the colors, maiteys! Cast off the lines, and set sail on the 'emerald isle'!
