Water Level Monitor

Enlarge Image Image Gallery PHOTO 1: The sensor tube you'll be submerging in your tank. PHOTO 2: Ten 220 k-ohm resistors wired in parallel. PHOTO 3: The back of the meter, wired in parallel with a zenner diode.   PHOTO 4: The meter in its wall-mounted wood base. PHOTO: T.J. BYERS

The amount of water that's held in storage at my remote homestead is of critical interest to me since I'm well out of reach of the nearest public utility. But I also have far more to do in a day than play nursemaid to a cistern. So, at the height of last year's dry season, when my water worries were at their worst, I put together a remote water level monitor for my tank.

Based on a few common electronic components, my device has proven to be infallible over the last 14 months. And now, monitoring the level in my holding tank — which used to involve a wearying and time-wasting walk up the hill — is as easy as glancing at my living room wall.

Water Conducts

Don't be intimidated because a few electronic gizmos go into the construction of my device. The components are easy to install, and the water sensor itself is simply based on the fact that water does a better job of conducting electricity than does air. If you place evenly spaced electrodes inside of the tank, wire them in parallel, and then apply current at the container's bottom, the amount of current returned to the meter will be in proportion to the number of electrodes that are in contact with the conducting liquid.

The Sensor Tube

You can begin building your own water monitor by assembling the sensor tube, which consists of a piece of 1" Schedule 40 PVC pipe (three inches longer than the depth of the tank's maximum water level) and eleven No. 10 stainless steel, self-tapping sheet metal screws. The fasteners function as electrodes, and you can determine the proper position for each one by dividing your cistern's maximum water depth into ten equal segments. (For example, if the water is 30 inches deep, there should be a mark every three inches.)

Once you've located the points, drill a 3/16" hole at each spot . . . as well as an eleventh hole, positioned halfway between the bottom of the PVC and the first mark and 1/4 turn of the pipe to the left. (This opening will accommodate the "hot" line.)

When that's done, prepare 11 lengths of 16-gauge wire. The first should be about a foot longer than the tube, and each successive section should be three inches shorter than the previous one. With the exception of the "hot" wire, it makes no difference which lead is connected to which resistor ... so color coding isn't necessary. However, it's a good idea to identify the "power" line by tying a knot in its end. Complete the wire preparation by trimming 1/4" of insulation from both ends of each conductor.

You'll find it easier to string the wires into the tube if you start with the longest ("hot") wire first and work up . . . so slide the knotted length into the pipe and pull its stripped end through the bottom hole. Then carefully thread one of the screws into the hole so that it traps the wire and makes a good contact. (Be sure not to break any of the tiny metal strands with the sharp threads of the fastener.) Repeat the same procedure for the other ten wires, until the far ends are protruding from the top of the pipe.