The phrase "water samples" refers to small amounts of water that are collected and tested to understand its quality or characteristics. Full definition
The team collected water samples from the lens, and then kept drilling until reaching the lake surface itself. (sciencemag.org)
That means the team could immediately collect water samples to test for bacterial populations from areas that were threatened by the spill but had not yet been contaminated. (newscientist.com)
It can take weeks to get results on the level of bacteria in water samples. (nreionline.com)