If I remember correctly, this type of study is inherently flawed because it just measures how long fluids stay in your body before you urinate, which is a useless metric. There is no benefit to a fluid staying in your system for a longer amount of time than the equivalent amount of a different fluid. Please correct me if I am wrong.

Thing is, why does it matter if something exists that hydrates you better than water? Water is abundant and practically free - at least orders of magnitude more free than any marginally better substitute. You don't need a precise and refined strategic hydration strategy. When you get thirsty just drink some water, you'll be fine.

edit: yes, this does not cover edge cases like illness or working under very hot conditions

article links to a yahoo version of 2019 CNN which links to a 2016 study with a URL resulting in a redirect to the new standalone website for the journal now-declared-independence instead of a DOI I had to rescue from the archives which now links to the ScienceDirect hosting of the article instead: https://doi.org/10.3945/ajcn.115.114769 (Thankfully open (archive) access)

In summary, the present study describes a novel tool to enable the objective assessment of the effectiveness of beverages to maintain hydration status. The BHI is reproducible and the pattern of response for a range of commonly consumed beverages is consistent with what is known about the effects of their constituents on water balance.

My husband and I were having lunch in a diner last weekend and by the bar they had a display cooler selling Smart Water. I over heard the lady next table over tell her friend: "oh I need to get some of that before we go. ITS GOT ELECTROLYTES!" she said, unironically. I nearly choked on my lunch. Lol

When it comes to alcohol, stronger forms, like whiskey, for example, actually dehydrate, while beer shows better results.

So, drink beer with my whiskey. Got it.

Didn't the University of Florida figure this out in the 60s and why Gatorade exists?

Not only does it quench your thirst better, it tastes better, too, idiot!

results like this, always makes me think, who paid for the study?

Yeah, nothing I crave more after running 5k than a tall glass of… milk? 🤮

But water does hydrate you, and its free/cheaper than anything else.

2/3 of the world is lactose intolerant so milk can't be the best for hydration

When it comes to alcohol, stronger forms, like whiskey, for example, actually dehydrate, while beer shows better results.

I'm replacing water with beer the next time I run a marathon.

/this was a joke. i don't run

BRAWNDO!!! IT’S GOT WHAT PLANTS CRAVE! ELECTROLYTES!

Hahahaha!! I love that movie!!!

But tap water has electrolytes, right? That's why we get electrocuted.

100% pure water does not conduct electricity, but who uses that?

Yeah, a lot of people don't realize that electrolytes are just as important for hydration as water. Especially if you're doin some heavy activities and sweatin buckets. You lose so much potassium in effort sweat, and you'll just start locking up without it.

ITT: hYdRaTe WiTh MiLk!?

Isn't milk more "liquid food" than a drink? It's meant to provide full nutrition to young, not provide fluids to an adult. Humans drinking milk in adulthood is the weird part.

Food hydrates you best

Real Cutting edge stuff here in this paper from March 2016:

A randomised trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index

Ronald J Maughan, Phillip Watson, Philip AA Cordery, Neil P Walsh, Samuel J Oliver, Alberto Dolci, Nidia Rodriguez-Sanchez, Stuart DR Galloway

Published in The American Journal of Clinical Nutrition in March 2016.

Abstract

Background The identification of beverages that promote longer-term fluid retention and maintenance of fluid balance is of real clinical and practical benefit in situations in which free access to fluids is limited or when frequent breaks for urination are not desirable. The postingestion diuretic response is likely to be influenced by several beverage characteristics, including the volume ingested, energy density, electrolyte content, and the presence of diuretic agents.

Objective This study investigated the effects of 13 different commonly consumed drinks on urine output and fluid balance when ingested in a euhydrated state, with a view to establishing a beverage hydration index (BHI), i.e., the volume of urine produced after drinking expressed relative to a standard treatment (still water) for each beverage.

Design Each subject (n = 72, euhydrated and fasted male subjects) ingested 1 L still water or 1 of 3 other commercially available beverages over a period of 30 min. Urine output was then collected for the subsequent 4 h. The BHI was corrected for the water content of drinks and was calculated as the amount of water retained at 2 h after ingestion relative to that observed after the ingestion of still water.

Results Total urine masses (mean ± SD) over 4 h were smaller than the still-water control (1337 ± 330 g) after an oral rehydration solution (ORS) (1038 ± 333 g, P < 0.001), full-fat milk (1052 ± 267 g, P < 0.001), and skimmed milk (1049 ± 334 g, P < 0.001). Cumulative urine output at 4 h after ingestion of cola, diet cola, hot tea, iced tea, coffee, lager, orange juice, sparkling water, and a sports drink were not different from the response to water ingestion. The mean BHI at 2 h was 1.54 ± 0.74 for the ORS, 1.50 ± 0.58 for full-fat milk, and 1.58 ± 0.60 for skimmed milk.

Conclusions BHI may be a useful measure to identify the short-term hydration potential of different beverages when ingested in a euhydrated state.

Beer

Milk was a baad choice