The sewage treatment fee is approved in accordance with the principle of compensating the operation and maintenance costs of the sewage network and sewage treatment facilities and making a reasonable profit. The tax levied on the sewage treatment fee is the income from engaging in qualified environmental protection projects, which is exempted from enterprise income tax from the first to the third year, and halved from the fourth to the sixth year, starting from the taxable year in which the project obtains the first production and operation income.