The Google Pixel isn't waterproof, but from what I've read on various websites, Google has confirmed both Pixel phones have IP53 rating, the same as the HTC 10. The number 3 means that the devices is protected against spraying water (not splashing water and obviously no immersion). The number 5 means that it's Dust Protected, but ingress is not entirely prevented.
So all in all, the Google Pixel has water-resistant to some degree but it's not waterproof like the Samsung Galaxy S7 for example that carry an IP68 rating, which means it has a high-degree of water-resistant and can be submerged in water to some degree as stated by the IP rating).
Keep in mind that the IPX3 certification means that the device is tested when water spray comes from up to 60 degrees from vertical for 5 minutes. It's good that we can at least know to what degree the Google Pixel phone is protected from water and I think these tests should be done for most mid-range and high-end devices, so the customer can know the degree of protection ahead of time before buying the device. That said, usually when the device is waterproof (to some degree), the phone manufacturer will mention it, and if not, you can always call of chat wit the customer service of the device's company and ask them that question.
So don't dunk your Google Pixel in water and don't rely on it to be fully protected from dust particles, because it doesn't carry that high degree of protection. I am quite disappointed to see that the Google Pixel, which isn't a cheap phone, and come close to the price of some of the other high-end devices it competes with, isn't waterproof. It's the end of 2016, and we can see that most of the leading phone manufacturers are waterproofing their high-end devices or at least giving them a very high degree of protection against water, including Apple with its new iPhone 7 which is IP67 certified.