Translation:I need a bank account to open a business.
My questions were (see above): 1) Is "rekening" always strictly associated with banks? 2) Looked it up and "account" also means "akun". When do you use "akun"?
I am glad you asked about hydro. It is a short for hydroelectricity (listrik) and the term, I believe, is used in English speaking countries. In some countries people also pay for water utility and you pay the bill usually through an account with the municipal government.