Use different passwords for each of your accounts. If someone figures out the password of one account, that person may be able to access your other accounts too. Moreover, as every site does not take security too seriously, so hacking some sites may not be too difficult.
The administrator may have access to the password you used in your account with their service. What if an administrator tries to log in to your account with another service with that password? Your security will be compromised if you use the same credentials for both services.
If it is too difficult to manage different passwords for each account, use different passwords for sensitive accounts and another in multiple non-sensitive accounts.