What is the most precious resource on earth? Gold, diamonds, or rare minerals? These items might come to mind first, but we can live without them. No, it’s water, something that every person needs to survive. Even though it is the most precious resource on earth, water is also a badly wasted and abused resource.

It’s interesting to note that although the earth is comprised of 70% water, people worldwide still don’t have access to enough clean and safe water to drink. As a matter of fact, freshwater makes up just 3% of the water supply, but less than 1% is freely available. The rest is tied up in in icebergs, glaciers, and snowcaps. This leaves us in the midst of what the United Nations is calling a “water crisis.” The issue is definitely not a lack of water, but a lack of clean water. In fact, millions of people die each year from preventable diseases, after drinking water from an unsanitary source.

Even in the United States, where water-borne illness is not a major concern, clean water supplies are finite and wasted water has negative consequences. Leaks can cause everything from rotten floors to mold infestations, to significant flooding events. Consumers pay higher bills; municipalities must create additional infrastructure such as dams and aqueducts that impact the environment.

Let’s look at the facts:

• 3.9 trillion gallons of water are consumed in the United States per month.
• More than one trillion gallons of water leak from U.S. homes each year.
• 10% of U.S. homes have leaks that waste 90 gallons, or more, per day.
• Every day leaking pipes lose an estimated 7 billion gallons of clean drinking water which would fill over 11,000 swimming pools.
• There is an $11 billion annual shortfall to replace aging water facilities in the U.S.
• Each year 240,000 water mains break in the U.S. ().

Measuring Lost Water

So now we ask, “How can someone allow their home to leak 90 gallons of water a day?” The problem may not be bad intentions or deliberate negligence, but rather bad measurement technology. Today’s mechanical water meters have poor accuracy, especially at low flow rates where they typically don’t register any flow at all. Over time the meter’s performance and accuracy degrade even further.

The minimum flow-rate requirement in the U.S. for cold-water meters is currently 0.95 liters per minute, which adds up to 1,363 liters/day. This requirement, established by the American Water Works Association (AWWA), has not changed since the first standard was proposed in 1921. Based on this standard, any flow below 0.95 liters per minute is measured as zero water use. Now it becomes clearer how a trillion gallons a year is lost and invisible due to leaks in U.S. homes.

Is there any good news?

Yes, the Natural Resources Defense Council (NRDC) in partnership with U.S. utilities submitted a proposal to reduce water waste by lowering the minimum measured flow rates to 0.2366 liters/minute (0.01m3/hour). That is good progress, but today’s static mechanical meters cannot meet this improved standard. Fortunately, ultrasonic metering technology can easily measure the proposed lower flow rate.

Ultrasonic flow-metering technology can detect flow rates below 1 liter per hour, which is 60 times better than current U.S. standards. Ultrasonic flow-rate detection uses silicon connected to two piezo elements. A pulse is transmitted from one piezo sensor to the other, and the delta in pulse times of flight (i.e., how long it takes the pulse to travel from one sensor to the other) reveals how fast a liquid is flowing between the sensors.

This ultrasonic technology was once reserved for very expensive water meters used in water distribution systems or industrial flow-monitoring systems. However, advances in sensor technology and more integration of the silicon-based analog front-end (AFE) have made this technology economically viable for mass deployment of utility water meters. The yield forecast is a 10x improvement over today’s traditional mechanical meters.

Adoption of ultrasonic metering technology will enable the detection of very low flow rates to better identify leaks and water waste. So, what’s holding it up? A combination of public education and legislative pressure are needed to move society away from their grandfather’s water meters. The resistance to the rollout of smart electricity meters demonstrated what can go wrong when the public isn’t bought in to new technology, no matter how beneficial.

How can I learn more?

To see an example of an ultrasonic flow meter, visit Maxim’s REFDES70#: High Precision, Long Battery Life Heat/Flow Meter. This reference design is based on the MAX35101, a time-to-digital converter with an integrated AFE. It performs time-of-flight difference measurements on upstream and downstream ultrasonic pulses. The accompanying documentation includes a detailed explanation of how the flow rate is calculated using the ultrasonic measurements.