Many costomers ask this question to us.
"Miyakojima's water is very soft, isn't it?"
Soft water means that it contains less minerals and people feel it moisturizing and tasty with coffee or tea.

Actually, it is incorrect. Water in Miyakojima is extremely hard. It contains huge amount of minerals because of circumstance of soil.
This island is made by ancient coral. It contains much calsium carbonate and other minerals. 
In the other hand, the water supply depends on "Underground Dam". So existance of Underground Dam makes this island's water supply special.

Let me explain about Underground Dam. 
As I witten before, this island have a thick ground of calsium carbonate. It can melt very slowry with rain or other water. Then, through a long time, large vacant rooms were created under ground. It is the limestone cave.
At the same time, the ground have a lot of small holes because of its melty feature so that rainfalls get into under ground and not make river.
Usually, limestone caves under ground have exit to the sea. And water came from ground gets away through this exit.
BUT technology got the way to privent to water getting away. Somehow, they blocked the exit and succeeded to store enormous amount of water in the caves.
This is the Underground Dam in Miyakojima. The one of the most important life line.

The Underground Dam solved most of water problems but it has other problems still now.
One of them is that water is extremely hard. It is simply because water is stored in the cave made by calsium carbonate. Too much calsium is melt into water.
Governmets made a facility to reduce the minerals form water supply but it is not enogh, it is still too hard.
This water couses diarrhea if you drink much. And other problems are clogging pipe lines, making skins too dry in shower, tasting not good to drink…etc.
If you boil this water in a pot and make it evaporated completely, you will find the pot's inside white. This white remain is calsium and it couses problems.

In these days, people came to install "water softner" when they build a new house. It is a equipment fairly expensive. But they do not have to worry about the troubles of water and costs to fix pipe lines or other water equipments. 
So do our house.
We have the water softner.

So this is the answer.
In our guest house, you may feel the water soft just because of the water softner.
Many costomers had been glad to use this water, especially for women. This water makes condisions of skin or hair good.

There are other stories of the water in this island. I may write them someday.
Bye.