It's accessibility in the sense that computer input methods popular in the West can't generate them. As far as I know, there's no way to get my computer or phone keyboards to produce 水 without switching to one of the CJK input modes.
On Mac, at least, the "Emoji keyboard" accessible through Cmd+Ctrl+Space in all standard text controls makes it possible to add basically any character in Unicode if you know its name. For example, you can type "water" to get ⽔ (along with other characters, like the water droplet emojis). I use this often to type the Greek beta symbol, for example.
...and then when you look it up that way, if you note that it is U+2F54, and if you have your your input source set to "Unicode Hex Input", you can enter ⽔ by holding down the option key (⌥) and typing 2f54.
As far as I know this only works for characters in the BMP, but for such characters it may be faster than picking them from that cmd-ctrl-space popup.
If you don't have that input source available, you can add it via the "Input Sources" tab of Keyboard preferences. There you can also enable showing the input menu in the menu bar giving you an easy way to switch between "Unicode Hex Input" and your normal input source.
