Clamp-on water meter?

Question

My region is experiencing a drought and I'd like to know how much water my household is using so we can be sure that we're minimizing our water use (which is good to do even in normal conditions). However, my home is in a multiple unit development, where none of the dwellings have an individual water meter, all units get water from the central meter.

Is it possible to make or buy a clamp-on meter for home use that I could just clamp on my copper inlet pipe to give me a sense of how much water I'm using? Ideally something electronic that I could read and record automatically, but even a local display would be fine.

I've looked around a bit online and found a number of products that are oriented toward the industrial market, with prices to match (~$1000 and higher), like these:

Ultrasonic Flow Meters Ultrasonic flow meters utilize sound waves to measure the velocity of a fluid from which the volumetric flow rate can be calculated. Unlike most flow meters, ultrasonic meters do not include any moving parts and thus are more reliable, accurate and provide maintenance free operation. Since ultrasonic signals can also penetrate solid materials, the transducers can be mounted onto the outside of the pipe offering completely non-invasive measurement eliminating chemical compatibility issues, pressure restrictions, and pressure loss

I'd rather not go through the hassle and expense of having a plumber install an in-line water meter (and I'm not even sure the HOA would agree to allow me install it since the most accessible part of the water line is in a common area), so I'm looking for something that doesn't need to be permanently installed.

Answer 1

I think the cheapest option would be a calorimetric flow meter. Description from engineering toolbox

The calorimetric principle for fluid flow measurement is based on two temperature sensors in close contact with the fluid but thermally insulated from each other.

One of the two sensors is constantly heated and the cooling effect of the flowing fluid is used to monitor the flow rate. In a stationary (no flow) fluid condition there is a constant temperature difference between the two temperature sensors. When the fluid flow increases, heat energy is drawn from the heated sensor and the temperature difference between the sensors is reduced. The reduction is proportional to the flow rate of the fluid.

Response times will vary due the thermal conductivity of the fluid. In general lower thermal conductivity requires higher velocity for proper measurement.

The calorimetric flowmeter can achieve relatively high accuracy at low flow rates.

In you case, you would have two sensors clamped on the pipe (maybe a band). The thermal conduction of the pipe would distort your measurement.
You could build one yourself, and test it on a pipe exactly like the one you clamp it on with a mechanical inline flowmeter (that you would have to buy, but those are cheap). The nice thing is that the exact flow regime is irrelevant, as you measure the mass flow rather than a pressure drop or similar.

While I'm convinced that this is the most doable clamp-on flow-meter for a DIY project, it may still not be very doable.

Answer 2

I think that, as you suggested, an ultrasonic flow meter would be great. They simply "clamp on" to what you want to measure, no interruptions. Ultrasonic flow meters do not move and therefore should be the most accurate and reliable option.