What I learned:
Mugicha is drunk at nearly the same rate as water in Japan - and that's the whole point - The clearest framing this month came from @ScrubbedChungus on X: "NOTHING is better than a cold glass of iced tea when it's hot out... this is mugicha, it's a caffeine free barley tea that is probably consumed at nearly the same rate as water in Japan." That's the mental model outsiders miss - mugicha isn't a "tea" you choose over water; for many households it functionally is the water. It's the default liquid in the fridge, not a treat.
The reason it beats plain water is minerals, and the reason it beats green tea is caffeine - The practical case, per GreenTea.st, is that mugicha carries potassium, magnesium and phosphorus - so it rehydrates better than plain water when you're sweating through a humid Japanese summer, which is why athletes and outdoor workers reach for it. And unlike green, black, or oolong tea, barley is a grain, not a Camellia leaf, so it has zero caffeine. That's the deciding factor for the group that matters most: it's the default drink handed to babies and small children in hot weather, because it hydrates without any stimulant.
It's less a beverage and more a domestic ritual tied to childhood - The most-liked post in the set, from @kunoichi_jp_, leans entirely into the emotional register, not the health one: "summer sometimes tastes like tea with no sugar... A glass pitcher in the fridge. Ice cubes. A kitchen in the afternoon. Children coming home sweaty from outside. It is not fancy. It is not dessert. It is just cold tea waiting for someone to come home." The same account, replying to a curious foreigner, notes the deeper landscape: "In Japan, tea is not only hot tea. Mugicha, oolong tea, hojicha, green tea… the cold tea world is very deep."
The cold-brew-by-the-pitcher method is deliberately effortless - The actual technique, per Senbird Tea and echoed in the Japanese TikTok how-tos (水出し麦茶 作り方) the engine surfaced: drop a barley tea bag (or 15-20g loose roasted barley in a mesh infuser) into a glass pitcher, fill with cold tap or filtered water, refrigerate 4-8 hours, done. No boiling required for the summer version. It's forgiving to the point of being foolproof - it won't turn bitter even if you leave it overnight, which is exactly why it became the everyday household drink.
It's institutionalized enough to have its own holiday - Barley tea is entrenched enough that June 1 is officially "Mugicha Day" (麦茶の日), designated back in 1986 by the barley tea manufacturers' cooperative, and a MyVoice survey has it as the #1 summer drink for 40%+ of Japanese respondents, per Unseen Japan. A drink this ubiquitous is now mostly mass-produced, with artisanal roasting increasingly rare - a handful of traditional Tokyo roasters are all that remain.
KEY PATTERNS from the research: 1. Mugicha is positioned as a water-replacement, not a tea-choice - "consumed at nearly the same rate as water" - per @ScrubbedChungus 2. Two-part "why not the alternatives" logic: minerals (potassium/magnesium) beat plain water for sweaty-day hydration; zero caffeine beats green tea, making it kid- and baby-safe - per GreenTea.st 3. The emotional pull is nostalgia and domestic routine - the pitcher in the fridge, kids home from outside - not health claims - per @kunoichi_jp_ 4. The canonical prep is cold-brew (mizudashi): tea bag in a glass pitcher, cold water, 4-8 hrs in the fridge, near-impossible to mess up - per Senbird Tea 5. It's a cultural institution - June 1 "Mugicha Day" and a 40%+ favorite-summer-drink survey figure - per Unseen Japan