The legal basis of the sewage services charges is provided in the Sewage Services Ordinance. Sewage services charges have two components: the Sewage Charge (SC) and the Trade Effluent Surcharge (TES). The SC aims at recovering the cost of collecting and treating wastewater at or below domestic strength. The TES aims at recovering the additional cost of treating trade effluent with pollution strength exceeding that of the domestic sewage.

The sewage services charges are calculated based on water consumption readings provided by the Water Authority excluding water supplied specifically for flushing purposes. Only consumers whose premises are connected to the public sewer system are liable to pay sewage services charges.

Sewage Charge (SC)

The sewage charge is calculated based on water consumption readings provided by the Water Authority (excluding water supplied specifically for flushing purposes). Consumer of each domestic account is entitled to exempt from paying SC for the first 12m3 supplied in each 4 monthly consumption period. For the 13 years from 1995 to 2008, the unit rate of the SC per m3 of water supplied remained at $1.20 without any adjustment. During the period, many new sewerage infrastructures, including the major sewage treatment works at Stonecutters Island which serves a population of 3.5 million, were completed to provide better sewage services. Consequently, the operation and maintenance cost of sewage services has increased substantially. After the Sewage Services (Sewage Charge) Amendment Regulation 2007 was enacted, the SC rate started to increase by 9.3% per annum, until $2.92 at 2017. The SC rates are shown below.

For the trades listed in Schedule A, water would be consumed during the production process and hence the quantity of sewage generated would be less than the quantity of water supplied. Those trades are therefore entitled to a reduction of SC and the total SC chargeable to their accounts would be calculated based on 70% of the water supplied. The others are charged at 100% of the water supplied.

Trade Effluent Surcharge (TES)

Trades listed in Schedule B are required to pay TES in addition to SC because the pollution level of the wastewater discharged by them exceeds that of the domestic level. Under the TES charging scheme, the TES rates are determined by reference to the pollution level (in terms of Chemical Oxygen Demand (COD) values) of sewage generated by the respective trades. The prescribed generic COD values and the corresponding TES rates for different trades are also listed in Schedule B.

For the trades listed in Schedule C, water would be consumed during the production process and hence the quantity of sewage generated would be less than the quantity of water supplied. Those trades are therefore entitled to a reduction of TES and the total TES chargeable to their accounts would be calculated based on 80% of the water supplied. The others are charged at 100% of the water supplied.