100 m
A RapidH2O barrier 100 m long and 1 m tall can be built by 4 people using 2 pumps of adequate power in only 2 hours. Anyone having the experience with filling sandbags will agree that not even a hundred people can build a barrier half as long in two hours. And this requires having enough sand at hand.
Dismantling such a RapidH2O barrier will take half an hour less in the same number of people (i.e. approximately 90 minutes). No laborious tidying and removal of sand is necessary.