Making and Using a Water Level

The Most Accurate Level There Is

Posted by: Dale Williams on 6/24/99 in Reply to a question about a retail water level

Rather than buy a water level why not just take 20' of 3/8" ID (Inside Diameter) clear tubing, and attach it to a coffee can with a soldered on 3/8" OD copper tube. [If it's a one-time job, you can just put the end of the tube in a can or bucket and siphon water into the line.  I use a mop bucket, and tape the tube to the lip of the bucket to hold it in place.  Suck on the other end of the tube until water comes from the bucket into the tube and reaches the part lying on the ground.  Then, lay the tube on the ground until water flows out of the end. -- jim]

If you learn a few facts about water levels you'll find them far more advantageous and accurate than even a Builders Level, Transit, Laser Level, or spirit level. Not to mention it is a lot faster to setup and use and with only one person.

Does it shock you to hear that a water level is more accurate than a Laser Level or a Transit? After some explanation I believe you will feel the same way too. For one thing, the earth is not flat. Shocking? I know, but it's true. So what about a lake, is it flat? Nope. Let's say you were to setup a transit at one end of a bridge span of, say, 2 miles--something like the Evergreen Point Bridge in Seattle Washington. If a laser level, a transit or a 2-mile long spirit level were used to determine the level across the lake it would be off by over 26 inches on the other side of the lake. (Bowditch) Whose wrong the water in the lake or the laser level, the transit or the spirit level?

OK, now that I'm finished smarting off, let's see if I can get you some information on the use of a water level. There are two types most commonly used today: 1) the kind which a single tube that's clear at each end and normally requires two people to make the measurement and; 2) a tube attached to a reservoir with measurement end clear [Figure 1].

        Figure 1
Note: There's only one tube.  The dashed line illustrates putting the tube in a second location.

I use reservoir water levels like the Mays, Aqua Level or my personal own Folger's or any can or bucket on the job site. I've even used my Thermos. That's right all you have to do is put the line in the bucket and siphon the water out and you have a water level. Accurate to the thickness of the pencil line. The biggest trick is just making sure there is no bubbles in the line. Large bubbles anyway. Those little ones that stick to the side with freshly poured water are not a problem.

To use the water level there is a thing called a meniscus which is the primary source for determining when the setting is a gnat's buns level. The meniscus is created on the inside of the tubing because of the water's resistance and sticking to the inside walls of the tubing [Figure 2]-- it will be more pronounced in smaller tubing sizes. It is seen when the water is being drained back to the reservoir and will disappear when the water is flowing away from the reservoir toward the end of the tubing. You are at the most level point when, moving the tube up or down about 1/32 inch, you note the water going from flat to dimpling--the start of a meniscus.

Now here's why a reservoir should be used instead of just using a tube/hose filled with water. The level of the water on the reference end needs to kept the same. In any Water Level the reference changes level as you move the working end (measurement end) up-and-down. But, this change is MUCH less when using a reservoir. The amount the water height changes at the reference is determined by the ratio of surface area of the reference end to the surface area of the working end. A single tube has a one-to-one ratio -- both ends have the same diameter and thus the same surface area. If you're off 1/8" at the reference end, the measurement will be off 1/8". But, the 6" coffee can reservoir with the 3/8" ID tube has a surface area ratio of 256 to 1. To be off 1/16th inch with the 6" reservoir, the marking point would have to be 256 times 1/16th inch in difference. This means the water could be drained back into the reservoir or allowed to go closer to the end of the tube by 16 inches. In other words, the working end can move up or down 16 inches while striking a level mark or, between level marks, and only affect the measurement by 1/16". Shoot most unsharpened pencils are off more than that.

Here is just one more tidbit of information. The hose can go over obstacles without affecting the accuracy of readings. This means it can be higher in the middle than at each end. Just don't let the marking end go below the level of the water in the reservoir. What this mean is, let's say you have to do some markings inside a form for concrete. There is no need to have the reservoir inside the form it can be mounted on the outside, the hose draped over the edge and markings made for a level plane, from which any other desired level markings can be made for the finished pour. Another situation may be taking the hose up through a house and back to ground level to determine something about the existing foundation. Just try having the reference and working end set and then lift the hose somewhere down line toward the middle and see how much pours out. I'll just bet there won't be one drop.

I guess this was a bit of a dissertation but, in the end, I hope you find the information useful for any project you may do requiring an accurate level plane from which to work.

Here is just one more little tidbit of information. I have Stabila levels that are guaranteed to be accurate to 1/10 of 1 degree. Just how accurate is that? Well according to my Trig Plus II it is .20944 of an inch or 3.35 sixteenths of an inch in 10 feet. Guess what I use for all lay outs longer than my Stabilas.

A word of caution:  With the reservoir method, if any water spills out of the tube or reservoir you must start over, because the points marked before and after the spill be at different.  If you have a large reservoir and a tiny spill the error may not be enough that that you care.

Expect the water level to rise and fall in the tube when you first place the tube at a new location.  Just give it time to settle down.  If the tube is hanging above the ground such that it can swing this will also cause the water level to go up-and-down as long as the tube continues moving.

The reservoir method provides equal height reference marks -- a level plane. It doesn't directly transfer the height of an existing point.

Let's illustrate using the level (red) marks on the two posts in Figure 1 to locate the top/height of the shorter post on the taller left-hand post. Measure from the level mark on the short post to it's top then, measure this same distance up from the level mark on the taller post -- this new mark will be on a level with the top of the short post. -- jim

Here's another illustration of using a reservoir water level

Hugo writes:
I found if you add 3 to 5 drops of dishwashing liquid per gallon of water the meniscus issue is minimized.    It does not change the working of the level at all as long as the soap is mixed well (it tends to evenly saturate the water by itself anyway, but mixing is good insurance).    Since the meniscus is almost gone the level is much easier to read and transfer a reliable line to the desired surface.    
[Good tip -- jim] 

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