Laser levels are cheap but you have to get them set level before they are
accurate.. Just like a transit, you have to level it with a bubble..
You also need something steady to rest the lazer level in while your pivet
it to aim at each corner or reference point. Each time you pivet it you need
to check the level bubble..
So a cheap laser may not be any easier or accurate than a water level..
I have always use a long clear plastic tube filled with water, however the
last time I need this, I found a kit for use on a garden hose.. It's just
two 1' long plastic tubes that screw onto the ends of a garden hose..The
only problem here is you can't see if you have bunch of air trapped in the
middle of the hose..
When I had my mobile (mfg) home set up, they used a clear tube but they had
a 5 gal tank on a stand and the hose came off the bottom of that. Plenty of
volume so there was never any concern about loss of water.. The tank was set
up at a height for convenient reference and never moved for the whole
operation. Hose was long enough to reach all points under the house. Only
took one man, where a plain hose always required a second person to make
sure his end was on the basic reference point.
Water line levels are still used in most of the third world countries where
transits are few and far between.. An engineer or survyor may locate a
reference to start a building, even a multi story and the on site people
will use the water line level to measure from the reference.
My opinion and experience. FWIW