Yes, apparently.
We see someone in the bathtub be affected by the Swooping Evil venom. Their face goes blank in a way that implies the venom took effect. We also see people drinking water forget as well. There are also water collection tanks on top of the roofs. The wizards are seen fixing them along with the rest of New York. I'll check my copy of the screenplay for textual evidence. But yes, I'm guessing the venom got into the water supply somehow. So presumably, it would later affect people who were under an umbrella when they come into contact with the water in their water supply. For the people who did not either get wet in the rain, drink water, or shower, which would be a small fraction of the population of New York, there are some possibilities that I can think of. The first is, it's never mentioned exactly how long the Swooping Evil venom stays active for. It could remain active for long enough where it would be impossible for people to avoid interacting with water in some way for that length of time. The other thing is, the Aurors could still Obliviate whatever small part of the population had managed to somehow avoid any contact with water for however long it takes the venom to become ineffective.