For completeness I propose an answer allowing to store both your account ID and password.
Solution 1: Store account in the Emacs init file
Append/add to your Emacs init file:
(setq erc-nick "my-nice-id")
(setq erc-password "my-nice-pw")
Note: You will get an y/n
query to accept default password (i.e. my-nice-pw).
Solution 2: Store account in an external storage file
To avoid sharing your sensitive data when/if you share your Emacs init file or to store your data in a more secure directory, you can store your account data in an external file. Append/add to your Emacs init file:
(let ((acc (read-lines "~/.my-erc-account")))
(setq erc-nick (car acc))
(setq erc-password (nth 1 acc)))
where ".my-erc-account" contains:
"my-nice-id"
"my-nice-pw"
Place and name this file as it is more convenient for you and adjust the read-lines
argument accordingly.