I'm in the mid-Atlantic region so our winters aren't as bad as further north, but this has been a cold one for us and cold weather does sometimes present challenges, especially if you're caught unprepared. The focus of this post is water!
Keeping your horses drinking in the winter is huge. Hot water in the barn helps a lot! I have a 10 gallon water heater that fits under the sink and produces enough warm water to give three horses at least one warm bucket. (I originally wanted a tankless heater but the plumber said it probably wouldn't produce enough hot water to meet my needs. When it's below 30 degrees, I fill one bucket with warm water when I bring them in from the field between 4 and 5 pm and a second bucket when I do night check around 9 or 10 pm. That encourages drinking at two different times and keeps the buckets from freezing longer at night. (Bucket cozies are also helpful.)
As for outside, if you can have an electrical outlet near your water source that will save you lots of time and effort. If you're installing new water lines, ask the plumbers to drop some appropriate electrical wire in there, even if you're not sure you'll install an outlet right away. It's always better to have it for later! I did that then bought this outlet intended for landscape lighting from Amazon and wired it. It's been extremely useful since the temperatures dropped. I put the 5 gallon buckets away and set a 16 gallon heated water tub on the ground, so even the donkey has access to water that's kept above freezing. They especially need extra water outside when they're eating mostly hay. I was worried the yearling would step in the tub or try to play with it and yank the cord out, but so far so good. It's a lifesaver! Another alternative is an automatic waterer designed for cold-weather use, but I don't have any personal experience with those yet.
Remember to remove your hoses when they're not in use. I have a very short one (5-6') at the pasture hydrant and I just detach that and set it on the ground, pointing downhill. Even if it feels stiff or crunchy in the morning, it's functional right away because it's short enough to drain completely. In the barn, I have a longer hose that I keep coiled in a large but lightweight Rubbermaid container that used to be my traveling tack box until the lid was chewed by someone else's dog. When I'm not using the hose, I store it in the tack room in the container. The container keeps the water that drains from the hose off the tack room floor, and it's easier to drag in and out than a loose hose. I've seen other barns put hoses in the sink during the day but I wanted mine out of the way.
Relatedly, have a plan in place to keep your pipes from freezing in very cold weather. Insulate your tack room walls and floor if possible. If you do that, pay a little more for higher-quality windows intended for use in insulated rooms. My tack room has insulated walls and an upgraded window, and I have not had to use a heater yet to keep the room above freezing (the possible fire hazard makes me nervous). Tonight will be in the single digits so I will stick a shielded light bulb under the sink where all the pipes are and maybe leave the sink dripping too.