Other mistake: On Caroline's uniform, you see the American flag patch on her right arm (I think it's her right anyway). The flag is backwards. Flag patches worn by military and government officials always has the stars in the front with the stripes following.
Signs (2002)
1 other mistake - chronological order
Directed by: M. Night Shyamalan
Starring: Mel Gibson, Joaquin Phoenix, Abigail Breslin, Rory Culkin
Continuity mistake: In the scene where Merrill, Graham and the kids are returning home from town, and Morgan is holding his baby monitor to listen to the aliens, his fingernails are very long. When he gets out and climbs on top of the car to get a better listen, his fingernails are very short. (00:29:55 - 00:32:15)
Graham Hess: Everybody in this family needs to just calm down and eat some fruit or something.
Trivia: Ray Reddy (the man who accidentally killed Graham's wife), is the writer/director/producer of the film, M. Night Shyamalan.
Question: First, let me say that the aliens being affected by only the "contaminants" in the tap water seems to be wrong. Two reason: 1)The Indian vet mentions that they don't like water, and 2) the aliens were avoiding areas with large bodies of water nearby. My question is this: wouldn't humans, who are over half water, be toxic to the aliens? Even if they processed the humans with different equipment and took precautions to avoid blood or body fluids, wouldn't carrying off a sweaty person burn the aliens? Seems like a dangerous harvest.
Answer: It could be that they are affected by the chlorine in the tap water (humans are affected by chlorine to, just look at Mustard Gas) to a greater extent then humans. The vet is only speculating about the landing sites. And while it is true that humans are mostly water, it is saline (i.e. salty like sweat) and has different chemical properties to pure H2O.
Soylent Purple
Well water does not contain chlorine.