Security deposits are used to pay your bill, should you fail to pay it. Deposits are charged by all utility companies and are held on your account for 1 year. Once good payment history has been established (after the 1 year mark) your deposit is credited back to your account with interest (prime less 2%).
Your deposit may be waived if you can provide to Priority, a Credit Reference Letter from another Canadian utility company. You also have the option to sign up for Pre-Authorized Debit; which once completed, your deposit will be waived or returned.