New sensor tells you when it’s time for a drink of water

By Stephen Beech

A new wearable sensor tells people when they need a drink to avoid becoming dehydrated.

The non-invasive device is designed to measure a user's hydration levels continuously, in real time.

Data collected by the sensor is wirelessly transmitted to a smartphone, allowing users to monitor their hydration levels.

American scientists say it could keep a firefighter battling a blaze from getting too dried out, or just let an office worker know when it's time to refill their water bottle.

Dehydration can range from inconvenient to life-threatening, but it's difficult to track.

Study leader Professor Nanshu Lu, of The University of Texas at Austin, said: “Dehydration is a silent threat that affects millions of people every day.

“Our wearable sensor provides a simple, effective way to monitor hydration levels in real time, empowering individuals to take proactive steps to stay healthy and perform at their best.” ​

She says the device uses "bioimpedance" - a technique that measures how electrical signals pass through the body, to track hydration levels.

Using strategically placed electrodes, the sensor sends a small, safe electrical current through the arm. ​

Lu explained that how the electrical current flows through the body depends on the amount of water in the tissues.

She says water is a good conductor of electricity, so hydrated tissues allow the current to pass more easily, while dehydrated tissues resist the flow. ​

The research team conducted several experiments to test the device, including a diuretic-induced dehydration study and a 24-hour free-living trial. ​

For the dehydration study, participants took a diuretic medication to promote fluid loss, and their hydration levels were monitored using the wearable sensor and then tested against a urine sample. ​

The results, published in the journal Proceedings of the National Academy of Sciences, showed a "strong" correlation between changes in arm bioimpedance and body weight loss due to water loss.

Study co-author Dr. Matija Jankovic, a post-doctoral researcher in Lu's lab, said: “Our experiments demonstrated that arm bioimpedance is not only sensitive to hydration changes but also aligns closely with whole-body hydration measurements.

​“This means the sensor can be a reliable surrogate for tracking hydration levels, even during everyday activities like walking, working, or exercising.” ​

He said traditional methods for assessing hydration, such as urine tests or blood analysis, are often invasive, time-consuming and impractical for continuous monitoring. ​

Commercial hydration assessment devices usually require bulky equipment and stationary setups, limiting their use in day-to-day life.

Hydration plays a critical role in maintaining organ function, regulating body temperature, and supporting vital physiological processes.

But dehydration - a condition caused by insufficient water in the body - remains a common and often overlooked issue. ​

Even mild dehydration can impair cognitive function and physical performance, while severe dehydration can lead to life-threatening conditions such as kidney stones, cardiovascular issues and heatstroke. ​

But the researchers believe the new device also has potential applications in health care.

They say continuous hydration monitoring could aid in diagnosing and managing conditions such as kidney disease, cardiovascular issues and chronic dehydration. ​

And Lu says it could also help athletes "compete and stay healthy" on hot days.

She said that while the current version of the sensor tracks relative changes in hydration, future research aims to establish reference data for absolute hydration levels.

The researchers also plan to explore new designs, such as breathable e-tattoos or sweat-soaking wearables, to improve comfort and performance during extended use. ​

The team hopes to expand testing to larger groups and explore applications for other body segments, such as the forearm or thigh. ​

Lu added: “This is just the beginning.

“Our goal is to make simple hydration monitoring accessible to everyone."