CPAP

The most popular CPAP is ResMed. It uses 95 watts (100 to 240 VAC, 50-60 cycles) a two-prong plug, and a water tub.

It is small enough for my one checked bag. I wrap clothes around the machine and snake the tube in my checked in bag. For Japan, the questions are - do I need an adapter/converter and where can I get distilled water for the tub.

ELECTRICITY

One can NOT use the CPAP in the plane. It's maximum plug-in power is 75 watts. The AirSense uses 95 watts.

However, the AirSense 10 works fine in the hotels and ship without an adapter or converter.

DISTILLED WATER

In Japan, most travelers report that distilled water is difficult to find. The most common water is called Purified. It is not distilled. Here is what I have discovered.

Most Japanese CPAP users use purified water, so it must be OK. A physician read a few articles about CPAP use in japan and it seems they use distilled water and purified water interchangeably. I should be able to find purified water at a pharmacy. In places like Shinjuku, I'll find one on every block.

I can show this note 

CPAP人工呼吸器用の蒸留水又は精製水をお願いします。(Distilled or purified water for CPAP machine, please.)

FROM https://www.cpap.com/blog/cpap-water/

Deciding what kind of water to use with your CPAP shouldn’t keep you from experiencing a comfortable night’s sleep. While there are many opinions on this topic, one thing is for sure: distilled water is the recommended choice among all CPAP manufacturers. While using tap water occasionally isn’t ideal, don’t let it stress you out if you need to use it in a pinch.

Both while traveling over Europe and on a bike ride I used tap water. I have also used it for several weeks at home with no damage to the AirSense. The tub built up a residue which I cleaned out daily.

OTHER INPUT from AI (warning: They are not experts)

The problem is seisei-sui is purified water. It is not distilled water. We need joryu-sui. Distilled water has the minerals removed.

ChatGPT

Distilled water jōryūsui "蒸留水" can be found in the following stores in Japan.

- Supermarkets: Many supermarkets in Japan, such as Aeon, Ito Yokado, and Seiyu, typically have distilled water available in the beverage or household goods sections.

- Convenience Stores (Conbini): Chains like 7-Eleven, Lawson, and FamilyMart often stock distilled water along with other beverages.

- Drugstores (Pharmacies): Drugstores like Matsumoto Kiyoshi, Tomod's, and Kokumin often carry distilled water among their selection of health and household products.

Gemini 

We can find Seisei-sui "精製水" in the following stores

- Drug stores like Matsumoto Kiyoshi or Don Quijote

- Supermarkets in the pharmacy section

- Convenience stores like 7-Eleven or FamilyMart

CoPilot

In Japan, distilled water (蒸留水, jo-ryu-sui) is not commonly sold at drug stores. However, you can find purified water (精製水, sei-sei-sui) available for purchase. 

If you specifically need distilled water, you might have better luck looking for it at drug stores. 

If you’re in need of medium volumes of distilled water (around 5-20 liters), you can explore options like checking gas stations, or visiting motor goods sections in malls or major supermarkets. 

Purified water https://sm.rakuten.co.jp/item/4987286412726

About four convenience stores (7-eleven and Lawson) are within four blocks of  Conrad, Unfortunately, there no assurance that they will have Purified water and most likely will not have distilled water.