To establish credit with the District prior to provision of water service each customer shall pay a cash deposit of seventy-five dollars ($75.00) or the amount which the General Manager estimates will equal an average monthly bill, whichever is larger. The deposit, less the amount of any unpaid water bill, will be refunded on discontinuance of service or after the deposit has been held for 12 consecutive months during which time continuous water service has been received and all bills for such service have been paid without being delinquent.