In the case of pipes for domestic discharges, a fairly accurate assessment is possible, but for trade effluent it is far more difficult, and a generous assessment should be made to cater for the varying discharges of each industry.

• 生活污水的排放量可以得到精确的估计,但要估计工业废水的排放量就困难得多。各行业的各种不同的排放都要充分估计到。