The neighborhoods where I've lived in Tokyo have been fortunate enough to have actual onsen. Subsidized by public funds, they provide low cost (400 - 500 yen) lovely hot springs experiences, with the water reputedly good for various ailments and sometimes specifically beneficial for skin.
Some do have outdoor baths, and some even have views, though not usually ones in the middle of town. They are enjoyable, relaxing, and people frequent them as part of their regular lives, for entertainment and even as family outings.
But in the age of COVID, I haven't been to my neighborhood onsen in a fairly long while, contenting myself with the swimming pool sized "Grand Baths" (with fabulous ocean views) on various ferries, which have been deserted, again due to COVID. I've been missing it.
Furthermore, I've been having dreadful problems with dry skin and falling hair. Apparently, this is not unusual for foreigners in Japan. I've asked about the water from the beginning and been told it's perfectly drinkable and it doesn't taste badly at all. Tokyo Tap is quite palatable.
What it is, though, I've more or less just discovered, is full of chlorine and very hard. I've bought special products, got cream from the doctor, asked the dentist and at just a couple of weeks away from five years here have had no real solution.
Finally, though, I was perusing an expat group that was discussing this very issue and several people said the answer was not a dermatologist or an endocrinologist. It wasn't the presence of some dread disease or the need to order wildly expensive products from afar, but to buy a water filter for your shower! Best 1800 yen I've spent in a long while.
I haven't had my new water filter long enough to gauge its effect on my hair but the effect on my skin was immediate and fabulous. I love it and will never be without one again, and I have high hopes that the fall of hair will diminish, though it will never cease as humans do shed.
The few friends I've told about this have all acted like I must a little slow to not have tumbled to this before, or deduced it from the outset by osmosis or something. I mean, the doctor? The dentist? Who I actually asked? So in that respect this is a PSA. Get a water filter for your home shower! Immediately!
One of the things that is common at an onsen is women washing their usually long hair. Of course, everyone washes their bodies before entering the hot spring bath, but now that I think about it, everyone also washes her hair. Presumably the fellows do it, too, but the bathing parts of onsen are segregated, even if occasionally, in rural areas, the hot spring tubs aren't, so I've never seen boy bathing.
I wonder if many women don't frequent their neighborhood onsen for the specific purpose of washing their hair. Many people are regulars, sometimes with lockers, often with discount ticket books, with their own towels (you can rent them, but that costs) and little baskets or bags of their own toiletries, though shampoo, conditioner and soap are provided.
Since I enjoy the onsen experience, I thought they just liked it! Even though onsen are inexpensive, it's cheaper to wash at home, and just about everybody nowadays has a shower, tub and hot water, though that didn't used to be the case. Now, with my newfound knowledge of the dangers of regular municipal water for skin and hair, my eyes have been opened! It's not just for fun that they come! They also want to use the advantages of the hot spring water to benefit their creamy skin and glorious, flowing, long hair.