The Xiaomi Mi 6 features an anti-splash protective properties. This can make sure that the phone isn't damage when a small amount of water is splashed on it, but it does not support soaking and Xiaomi mentioned that you shouldn't use it in the shower. Furthermore, no professional waterproof test has been done to test how well the Xiaomi Mi 6 can withstand when submerged in water. Xiaomi warranty does not cover in damaged which is caused by immersion in liquid. So having a light degree of water resistant surely helps. I think that it was just covered with a water-repellent coating, but I am not sure.
I'm sure that there will be some Youtubers who will try to test this phone's durability to its limit and try to submerge it in a pool to see how long it lasts, but you should never try this yourself, as you might damage the phone. I think that Xiaomi should have released the Mi 6 with an IP68 water-resistant protection, because it is its flagship device, and we've already seen many high-end devices coming with this type of waterproof protection. It's not a deal-breaker, at least not for me.
This anti-splash resistant should protect the phone in case you accidentally spilled your coffee on it or if it got a few rain drops. A phone without this protection would probably got damaged from any water contact and penetration, so this extra water-resistant features is nice. You can find more detailed information on the official Xiaomi website or you can always contact the support to get more detailed information. I just know that I will treat the Mi 6 the same as my other phones and keep it away from water. If you want water protection, you should probably be looking for a waterproof case for the Xiaomi Mi 6. I have no idea if there are ones which are available for the Mi6 but just Google it and see if you can find something.