WAC 16-390-280
WAC 16-390-280. Payment and collection of fees and charges
(1) All fees and charges for services rendered are due within thirty days after the date of the billing statement.
(2) If payment is not received within thirty days, service may be withheld until the delinquent account is paid in full.
(3) The director may assess a penalty of eighteen percent per annum on all unpaid account balances thirty days after billing.