# Measuring real time water usage with live water pressure monitoring

My home started seeing high water bills recently. My water company doesn't provide live water meter readings. There is a water meter on the street which I can monitor while water is being used but I would like to build a more comprehensive system which can present live water usage on some screen. The end goal is to show how much water is being consumed at any given time, live.

I might be able to buy fancy smart water from the market and call it done but I would like to build the system myself. I am relatively skilled in electrical/electronics/computer engineering (my profession) and I have some basic knowledge of water pressure and related physics concepts.

I thought of implementing the system this way.

I will install a high resolution water pressure sensor on one of the taps inside the house. This will show me live instantaneous pressure into my house. Assuming no water is being consumed, this water pressure shows the water pressure level from the city to my house. Whenever there is some water use, I imagine that pressure will drop from a relatively stable baseline by some amount proportional to the flow rate. It wouldn't matter which tap in the house is draining water; I expect the sensor to show some pressure drop.

After the pressure is dropped, the city's main water line will attempt to recover the pressure to some extent (either fully or partially). This will bring the pressure to earlier baseline and even beyond the baseline because there is damping component that exists in the house piping before the water pressure can stabilize. I expect to then see some damped oscillations for this event; first starting with a pressure drop and then reducing oscillations until stability is obtained. The opposite scenario plays out then the draining tap is closed. This cause the water pressure sensor to register a pressure increase, which again after oscillations, gets to a baseline. I did this experiment, gathered the data and this is exactly what I see. I captured some graphs which you can see on this post (for a related albeit a different question: https://dsp.stackexchange.com/questions/68328/how-to-detect-a-signal-while-ignoring-another-signal-which-is-a-phase-shifted-ve).

I am aware that city's incoming water pressure is not constant (neighbors share the water line) but that water pressure disturbance would be high frequency random noise (many people using at any given time randomly). My problem now is how do I translate this data to a flow rate for my home?

Any insights?

I know that flow rate is proportional to square root of differential water pressure. I cannot install water pressure sensor before the city meter to get differential water pressure reading so I am looking for other creative ideas. Perhaps I can characterize the system (measures the impulse response) and then predict flow rate?

The city water system is designed to maintain near-constant pressure over a broad range of flow rates. Your instrumentation system will be fighting this, trying to dig a useful signal out of a system designed to minimize it. This is a waste of your time.

If you have access to the meter, why not just place a wireless surveillance camera on a battery inside the meter sump? Then you can call up the camera on your home computer and actually see the water consumption totals minute-by-minute and calculate the corresponding flow rates on the spot.

Accurate, and easy.

• Yes, the city will attempt to bring the pressure back to baseline. However, there is some delay involved before the pressure can be brought back. I am hoping to analyze this window and deduce flow rate. I suspect some control theory and/or damping system basics is what I am missing. Commented Jul 12, 2020 at 6:23
• go with the camera and save yourself a lot of trouble. Commented Jul 12, 2020 at 6:25
• I also wanted to add that I did try adding a simple camera system before doing all of this instrumentation. I could never get enough WiFi signal to monitor the live feed. The meter is some distance away from the front porch on the street and under some kind of a concrete cap. This basically cuts off the signal. Another option I tried was to put a camera (like dash cam) and record the meter display continuously but that isn’t live. The only option left then is to run a wire and bring the live feed directly into the home all wired. I am afraid of potential theft as wires make it obvious. Commented Jul 12, 2020 at 6:29
• You can buy flowmeters that accurately measure the gallons-per-minute rate at which water is traveling through a pipe. These are used in industrial processes and can be had in both analog and digital output. The digital models can be had in bluetooth-enabled form. their drawback is they cost thousands of dollars because they are industrially rugged, and they require cutting the water mains pipe and grafting in the device. However, you may find semi-DIY flowmeters in the world of arduino, raspberry pi or beaglebone devices as used by home-automation hobbyists. Commented Jul 12, 2020 at 7:05
• too bad the camera idea did not work! Commented Jul 12, 2020 at 7:05

I have a similar project in mind as you are doing but the purpose is to see the pressure output if there is a leak.

from what i read, the city pressure equalizes the small drop when a leak might be present. this would make it almost impossible to detect leaks using pressure sensor. What are your thought. Thanks