Measuring water level in tank, how long a distance, what cable to purchase etc.

I want to add water level sensors to three tanks I have. The longest distance away is about 200ft. I was wanting to know what is the best way to do this, and what cable to purchase for the job.

Do I keep the arduino in the house and then run two wires to the tank level sensor (which I have no idea on what it will be yet) or do I put the arduino at the tank then run a generated signal from it back to another arduino back in the house.

How long a line can I take a reading off of a sensor from? What type of cable would I need? Ethernet cable like cat5e or cat6, or just any old pair of wires, or shielded wire like used with servos and steppers or what?

For the sensor end, I am thinking of using a length of pvc pipe that has a float that is attached to a string that is then wrapped around a wheel and encoder or sensor etc. That is one idea. I see you can do it other ways too.

So I just want to find out what cable to purchase to run through the conduit that I have already layed in the ground.


Over those distances, you may need to think about using RS485 serial communications. You can get inexpensive adaptors for that. Each sensor would have a small Arduino like Mini and an RS485 adaptor. They can share the same wires, because RS485 is a networking protocol. Obviously shielded cable would be more likely to work, but you might get away with unshielded. You will have to experiment.

As for the sensors, maybe ultrasonic sensors could measure the distance to the surface of the water. Or fit a float on the end of a long pole. Measure the angle of the pole with an accelerometer and calculate the water level from the angle. Any circuit inside the tank will have to be well protected from corrosion by condensation.

Another alternative would be to use RF to transmit data to the house. Each sensor/Arduino could be battery powered with a small solar panel.


The easiest and most reliable way to measure water level is to measure the water pressure at the bottom of the tank. I use Omega PX309 electronic pressure gauges with analog voltage output (0-5V) for this, and there would be no problem using 200 feet of 3-conductor cable to connect the gauge at the tank to the measuring station.

These gauges are a bit expensive, but are VERY accurate and so reliable that they will give many years of service. With them, it is easy to detect the slightest leak in the system. Note that if you connect the gauge to the tank outlet pipe, water flow will profoundly affect the reading, so measurements must be made when there is no flow.