This water meter is the most accurate level meter I have ever used (not counting micrometers or calipers).
It is easier to use and more accurate than using a bubble level and line, or tape measure. It can be done by ONE person, It can be used around corners from your reference point. I have used it to redo my entire perimeter drain system on my house and redo my back concrete patio to ensure slope and proper drainage, as well as level the pier blocks for my patio and shed to ensure they are all level.
It is CHEAP to build! It is SUPER ACCURATE! It is FAST to use!!
I searched the internet and specialty tool shops around my area and found similar but inferior products available for in excess of $100.
Here is a site that not only sells them but offers great explanations on how to use them.
I preferred building my own as it was a lot cheaper, and I had most of the materials already on hand.
http://watrlevel.com/index.htm
This cost me $15 for the tubing and ruler but has saved me thousands in man hours!!!!!

Step 1: Water Reservoir

Any water container will do, but the larger the container, the more accurate the reading over distance or height. Adding food coloring to the reservoir water will make it easier and quicker to read .
I used a recycled water container typically found in office water coolers, and installed a 1/4 inch plastic tubing approx 50 feet long through a rubber grommet in the side. This is only a pressure fit, but it was extremely tight so there has never been a leak.
The end of the plastic tubing I attached to a 24 inch long piece of recycled 1/2 inch conduit with a 24 inch ruler attached to it with zap straps. Do not plug the hole end of the tube!!!!! The longer the ruler the more latitude you will have with making measurements outside the zone of your reservoir limits.

Step 2: Measuring Limits

Before making a measurement lay down the ruler until water runs out the hole at the top of the tubing at the top of the ruler, and there are no air bubbles left in the line. This will ensure an accurate reading.
Next place the reservoir at your reference point. This point is normally going to fall between the highest and lowest points that would be possible during the extent of your measuring. This should fall between the highest and lowest points of your water level on your reservoir. On this example I have over 9 inches of reservoir height to play with.

Step 3: Reference Point

After placing your reservoir down DO NOT MOVE IT or you will have to redo the next steps all over.
Place the base of your measuring ruler on the point you want everything else to reference from.
This is called your base level or reference level.
Don't worry that your ruler doesn't read zero!
Keep the displayed reading in mind, or better yet write it down!
Here I am going to measure the height of a brick sitting on my concrete walk.
The reference point for the bottom of the brick is 46.5 cm.

Step 4: Measured Level

DO NOT MOVE THE RESERVOIR!.
Now move the measuring ruler to the point you want to compare to the reference point.
Here I placed it on top of the brick.
My new reading is 59 cm.
This a difference of 12.5 cm.
Here is a tape measure showing the same reading for the height.
This works excellent for slope and drainage.
If I know I want to have a slope of 1 inch per 12 feet the I measure out 12 feet and subtract the inch from my base reference level if I am looking for a downslope, or add the inch at 12 feet if I am looking for an upslope.
The neat thing about this is due to Pascal's law, it WILL WORK AROUND CORNERS!!!!!
The only reading you need to remember is your base reference, EVERYTHING is either higher or lower than that point.
I have found this to be accurate with 1/8 inch at 50 feet!!!!!!
A good trick to know is plugging the end of the plastic tubing with your thumb when relocating the measuring ruler to another point, and once there remove thumb and let the water seek it's level.
Try not to shake or flip the plastic tubing around before making a measurement or it will introduce bubbles into the line and change your reading. In that case, lay the ruler down below the upper reservoir level until water with no bubbles comes out. Then you must recheck your reference level and retake your measured level. Once you get the hang of this, you will wonder how you could waste so much time with a standard line and level technique!
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