My favorite home-made soda water

In weekdays, I stop drinking alcoholic liquids. It's because I found a great liquid, which is a home-made soda water, no sugar, no calorie and no preservative. I'd like to explain how to make it.
The items of needed.
 1. water
 2. equipment (in my case, I use twinspa by GREEN HOUSE CO., LTD)
       http://www.green-house.co.jp/campaign/products_special/twispa/

↑the bottle of twinspa. It allows us preserve the soda water in a refrigerator.

When making soda water, changing the part of cap to special part.

The special part. It can involve the small CO2 bottle.

You can see the bottle inside the special part.

The bottle can be bought in several on-line shops.