Since the canister of the Animalia Virus fell into the river, the government agency had been keep a lookout for any signs of it spreading. So far, it seemed to have been confined to only the river as well as being leaked into the irrigation system of the Brown Farm. However, tracking a waterborne virus is not an easy procedure, particularly with such an unusual virus such as this.
The Animalia Virus was originally designed to make animal meat more nutritious and increase fertility in farm animals. But after being cross-contaminated with another project's attempt to treat muscle disthrophy using gene therapy, the virus now causes animals to transform into muscular humanoid versions of themselves with increased intellect to boot. The only species that appeared immune to the virus were fishes and invertebrates. Humans were technically immune, but only if they were exposed to the pure virus. Exposure to an uplifted animal would turn a human into a similar human/animal hybrid.
Because of the virus's difficulty in being traced, there was usually no way to tell if the virus had contaminated a waterline. People who had contaminated water in their homes wouldn't even know there was a difference if the water only touched them. However, if they had a pet, the virus's presence would most likely be soon detected. For instance, Sarah Wesley and her family wouldn't know the virus was in their plumbing until Sophie comes home and puts infected water in her dog's water bowl.