Hydration tracking: Should you be tracking your water level?

Flouris is a little sceptical of sweat-sensing.

Referring to various unnamed devices that analyse sweat, which he has evaluated in the lab, he says, “Most of these products that we’ve tested do not show the level of accuracy that you would expect.” The results of his experiments are as-yet unpublished.

Sweat sensors, Flouris suggests, work best when worn during long bouts of physical activity – such as a marathon. But they struggle when the exertion is more varied and intermittent. Think a footballer switching from walking to suddenly running very quickly.

In response, Ghaffari says he and his colleagues have published peer-reviewed papers, external on the accuracy of Epicore Biosystems’ gadgets.

He acknowledges that analysing sweat loss over short intervals up to 20 minutes long “can be challenging” but says his company’s products appear effective for 30-minute, or longer, workouts.

Perhaps the most common hydration-focused products available are the smart water bottles that remind you to take a sip throughout the day.

“We try to make it fun,” says Cem Bakiş, head of business development at WaterH, which has a glowing ring that blinks in order to prompt its owner to take a drink. “You can add friends, you can earn points.”

Some smart water bottles work by estimating the weight of liquid in them, and how that changes over time as the drink inside is consumed. But WaterH takes a different approach.

Sensors detect when the water bottle is tipped at an angle, and also the flow rate of fluid as it leaves the vessel. The water bottle will immediately recognise when you’ve had a sufficient quantity of liquid, stresses Bakiş.

I point out that, while some reviews online are positive, other comments criticise the accuracy of these measurements. This is often an issue with how the device is calibrated, and easily rectified, responds Bakiş.

If you don’t want to take instructions in hydration from a water bottle, though, you always have the option of asking your toilet how things are going.

Vivoo makes a urine-analysing gizmo that sits on the rim of a toilet bowl, promising to help you understand your hydration “like never before”.

The device uses optical sensors to work out your “urine specific gravity” – a measure of urine’s density compared to clean water. The denser it is, the more dehydrated you are, generally. Small print on Vivoo’s website emphasises that its products are not intended to provide medical diagnoses.

Urine-based measurements are used to evaluate hydration in scientific studies, says Flouris. Though he notes that there can be some delay between a person entering a dehydrated state, and this becoming detectable in their urine.