Yes, I fully agree that the drainage system in Harappan cities indicates town planning. This can be substantiated with the following reasons:

First, the drainage system was one of the most distinctive features of Harappan cities, described as "the most complete ancient system as yet discovered." The careful planning is evident from the fact that streets with drains were laid out first and then houses were built along them, showing pre-meditated design.

Second, roads and streets were laid out along an approximate grid pattern, intersecting at right angles. Every house was connected to street drains and needed at least one wall along a street for domestic waste water to flow out. This uniformity reflects systematic planning.

Third, the drainage infrastructure was sophisticated. Main channels were made of bricks set in mortar, covered with loose bricks or limestone that could be removed for cleaning. House drains first emptied into sumps or cesspits where solid matter settled before waste water flowed into street drains.

Fourth, drainage systems were found not only in larger cities but also in smaller settlements like Lothal, where drains were made of burnt bricks while houses were built of mud bricks. Additionally, bricks of a standardised ratio were used across all Harappan settlements.

Finally, once platforms were in place, all building activity was restricted to fixed areas, confirming that settlements were first planned and then implemented accordingly.