While gas has a dangerous aspect to it that water does not, the principles are the same. Further, natural gas (esp. as compared to LPG) has a very small flammability window; in other words, heat, moisture and O2 have to be at a very close ratio to ignite. Plus, unlike LPG, CNG rises & disperses very quickly. In the US at least, residential CNG moves through the line at ~7-10psi. Common sense would dictate that gases (any gases!) are more leak-prone than liquids. Considering that your water lines are 50-100PSI vs. 7-9psi CNG, that comparison is a moot point.
My point is, as a fairly seasoned DIYer, as long as you measure, follow the laws of physics, test carefully and follow accepted code, there's no reason you shouldn't do your own gas lines, esp. since you can buy virtually any length of pipe pre-threaded at your local HD/ Lowes/ etc. Use a good light or get a helper if you're in a tough-to-access location (highly likely when running gas) Measure, note, measure again. Then buy more than what you need. Return what you don't need.
Finally (others will disagree, probably) I refuse to use teflon tape on pipe (any pipe, gas, water or whiskey) In my experience it's more problematic than job-specific "pipe dope" (comes in a jar w/ a brush in the lid) Beware, some is for potable water (galvanized pipe) and some is for CNG (the topic of this post) I don't know whether one is backward compatible with the other, and with the cost of a big jar being >$10, I'll buy whatever's specific to my application.
If you're doing a a CNG install, from a completely uninformed, uneducated and completely clueless DIYer, one thing I'd keep in mind is to put a trap in the line to catch various crap before it hits your appliance. When I recently installed a gas fireplace in my 1950s house, we used a compressor and blew out the (shutoff, disconnected) line and a metric assload(tm) of gaslinecrap(tm) came shooting out. Nasty stuff. Chunky. And it could cause problems for your new installation. Whether you DIY or hire it out, I'd strongly recommend you blast the line clear before spending money on any new gas appliances!
...and that's all I got to say about that...
Jim B.