Hi Darren, My workplace has forklifts and other machinery. We have water-coolers in all work areas. Our staff are given extra mini-breaks in between break-times with the sole purpose to re-hydrate. The rehydration message is emphasised during hot weather.

Hmmm not entirely sure of the factual basis of your article. For a start I think there might be some confusion between % of body mass lost and % of water lost. And no mention of sodium lost that needs replacing.

We can agree that dehydration can cause a gradual loss of important functions. But whether your average Forklift Operator gets to that point would be moot.

As for the outrageous assertion that dehydrated women perform better than men after drinking water. For a start they werent dehydrated - they had simply not drunk since the previous evening. "I feel a bit thirsty" does not equal dehydrated. And there were 25 women vs 9 men. The actual conclusion was "More specifically, water consumption appeared to have a corrective effect on the response times for thirsty individuals, bringing their speed of responding up to the level of non-thirsty individuals. "

"Drink to Thirst" is a pretty simple principle. As employers we should do what we can to ensure this can be done. But no two people are the same. And I know The Bottel Sippers won't appreciate it - but honestly. You can go quite some time without water before any detrimental effects associated with dehydration kick in.

I did make it clear in the article that it was a small sample and I simply repeated the results from the report. However, there wasn't space in the article to discuss other research that had been done about dehydration in vehicle drivers at Loughborough University that showed a doubling of driver errors over a 2-hour simulation period between drivers that were given a cup of water each hour vs drivers that were only given a few sips.
"Each driver was tested on one day when they were given 200ml of water every hour, and another day when they were given just 25ml – the equivalent of about five sips. On average, the participants made 47 driving errors while normally hydrated – but that number rose to 101 when they were on the “dry” day."

"Drink to thirst" is not a reliable principle. It's well-known that older people lose their sense of thirst and don't feel thirsty until they are already quite dehydrated. While thirst is not necessarily caused by dehydration, it is the primary indicator. I'd like to see your evidence that you can go for 'quite some time without water before any detrimental effects'.

Drink to thirst is a principle. You cannot set up hard and fast rules because every person is different, as is their working environments. When you say 'older people" it might be helpful if you referenced it as those broadly over the age of 65 - where it is a problem for those who live independently and living in a "heat wave" where their sensation can't be relied upon to signal the need to drink. Its a big problem in retirement villages and rest homes. Not one, I would have thought for your average forklift driver.

But back on topic "Other authors have found that the thirst sensation does not begin until about 1–2% of body weight or 2% of total body water has been lost."

As another broad principle you can estimate fluid loss through sweat at around 1.0 - 1.5 litre an hour under quite some exertion. Heres an exercise you can try at home. Jump on the scales and go for a walk or a run for an hour. Jump back on the scales and see how much weight you have lost. Most of it will be through sweat with some of it being loss of stored energy and respiration. (My last tested personal benchmark is 1.2kg an hour running in 25 degrees at 80+% max heart rate. Drink to thirst kicks in at about 50 minutes. C'mon forum members share your results!). Once you have tried this, then try it on your average forklift operator or driver. My money is on a result that won't come close to this weight loss.

Humour me - and lets say they loose 1/2 kg an hour in tough, but not extreme temperature conditions. That gives them 2 hours work with no detrimental effects. (In Christchurch here we do get such conditions - rarely in summer when the hot nor wester is coming through. Today its a balmy 14 degrees with gentle southery)

You want my citation - bare with me. "In this regard, there is disagreement in the literature about acceptable sweat rates for industrial workers. While sweat rates of 1.5–2.5 l/h have been shown over short periods (with peaks of 3 l/h), acceptable figures for a working shift are generally considered to be lower. ISO 793313 and Belding and Hatch advocate a limit of 1.04 and 1.0 l/h respectively for acclimatised persons, although ISO 988615 curiously states that “There is no limit applicable concerning the maximum sweat rate: the values ... adopted in ISO 7933 ... must be considered not as maximum values but rather as minimal values that can be exceeded by most subjects in good physical conditions”. Nunneley reports that humans can sweat indefinitely at rates of 1.5–2.0 l/h, while McArdle and colleagues recommended a limit of 4.5 l over four hours."

Lets agree to disagree and settle on an acceptable sweat rate of 1 l/h. Now that's going to be for an acclimatised worker - which is what our forklift operators will be (the exceptional one off hot days aside). That gives them an acceptable work period of 2 hours. I call that "quite some time" and we haven't even touched on "detrimental effects" at this point.

This paper here is interesting reading: https://oem.bmj.com/content/60/2/90#ref-21 . To save some effort it does involve research involving extreme working conditions (>28 degrees) and extreme work (underground miners). Your average Forklift Operator isn't going to come close to the condition extremes these miners work under.

Boils down to: under usual work conditions a cuppa at smoko will do the trick.