Bombarding the House
Every ripple conformed to a signal, a message of sorts the scouts used to transmit and receive messages. They were all Harmonisers attuned to the water element, able to use Water Qi perception. It was currently raining, creating a layer of water over the floor they walked on. Finally, it was easy creating ripples on the water.
They made use of this to communicate. It wasn't as if they had established it on the fly, but had been practicing the method since young. Only in such a way could they perform it without any errors. After all, they were birthed and nurtured with the intentions to be trained into scouts.