When it is a winter with snow, and you are in a situation where running water is not available in your building, it is a custom to ‘harvest’ water from what has fallen outside.
Please, so not eat snow. Do not just melt it and drink it. There are ways of using the snow for drinking and washing water, but to do so directly is not just cliche, it is dangerous.
If you find that you are in a home-bound situation where the water is not running, first, try to figure out why your water is not flowing. Frozen pipes, broken water mains and other things, including plants choking off the lines, are important to find before resorting to the water from snow. Try to deal with frozen pipes as soon as possible. There are many articles on that available, so I will not go too deeply into that. The best way to deal with frozen pipes is to know where your pipes are, and keep them insulated from both excess heat and cold.
If you cannot get the water running in the building, then look for alternatives. Bottled water is o.k. for many things, including flushing toilets. It costs money, and can be wasteful if you do not pay attention to what it is being used for. For every 24 hours, most people will use up to 300 gallons of water in a typical day. Showers, laundry, cooking as well as cleaning, watering plants, and just drinking add up. If you do not have access to a full water system, much of your typical water use will need to be curtailed. Use of sponge-baths for cleaning yourself sounds like a good alternative, but be aware that you can chill yourself easily that way. Put off cleaning, if you can. And invest in 5 gallon lidded buckets before you need them.
I highly prize my 5 gallon buckets, as well as the plastic cat litter containers I have access to. With the use of garbage bags, buckets with lids can be turned into waste receptacles. You have one flush once the toilet looses water. Switch to a bag-lined bucket as soon as you know the water is unavailable. Shower stalls or tubs are a reasonable place to put them for use, as not every garage is heated, or has space.
Buckets can also be used to keep highly soiled garments, towels and such until you can get them washed. Putting them out in the cold will keep most stains from setting, but can also bring animals to the bucket to investigate.
If you have a supply of non-bottled liquid, such as milk, soda and even beer, use that for drinking and cooking before dipping into your water supply to extend the water available. Just remember that most alcohol will speed dehydration, but is still useful. Disposable plates, especially paper ones if you have a fireplace, can keep the need to do dishes down to a minimum. Use of snow for washing can be done, starting with dipping the dirty pots and pans into the snow and heating the snow up with just a little bit of detergent or soap. This will make heated water to clean your wares, and help with anything that may have stuck on. Dump the used water down the toilet, if you can. The disposal in the sink may still have power and run, but it needs water to clear the pipes.
If you have figured out that your water and non-water supplies just are not sufficient, use several of the lidded buckets to gather snow. You can heat it to melt it, but most of the time, just having the bucket where it is warmer than outside will bring it to useable temperature. Just melted water will be cold, and will keep the area around it cold, too. Use this water for cleaning, watering plants and such, as long as there isn’t any salt mixed in. For all other uses, Heat, Cool, Strain.
Heat more water than you think you will need. Water is essential for humans and animals to survive. Bring it up to boiling for at least ten minutes. Many people say five minutes is enough to kill off bacteria, but you want to make sure when you are dealing with a shared water situation. Let it cool until it is down to about 100f, then strain the water through clean cloth(cheese cloth, usually) and then store the water in closed containers. All snow comes from the sky, formed around dust and pollutants. Once on the ground, everything can contaminate the water, and I, for one, do not want to find bird crap in my water as I am drinking it. If you are doing this with several 5 gallon buckets worth of water, a little chlorine bleach will keep things from growing in it, and you do not have to put in much to sanitize the water. A little bit of water, like a quart or litre, need only a few drops. A 5 gallon bucket is about 1 teaspoon of liquid bleach. Stir and let it sit for about 1/2 hour before use. Some people keep other forms of bleach, such as calcium hypochlorite, just for this type of emergency, but it is not essential.
As mentioned earlier, toilets will only have one flush once the water is off. I find that you can keep people from using that last bit of water by putting plants in the bowl and tank. The plants have water for a few days, and the toilet will not run dry. If you are in extreme conditions, such as a polar vortex slamming into your area, check to make sure that the toilet is not frozen before putting plants in the water. Not only can the water coming in freeze, the sewer can also be effected, blocking up and making a bad situation even worse. This is another reason to use your dish and other washing water and then put it down the toilet to keep that open.
DO NOT DRINK HOT TUB WATER. If you are lucky enough to have a hot tub, you have a ready supply of water for a while. BUT! Use it for washing, flushing toilets and other non-consumable options. The chemicals that are used to keep hot tubs sanitized will do the same with your innards, poisoning you and possibly destroying your digestive tract. Most households do not have the appropriate filters to be able to make hot tub water into potable water. The same goes for fish tanks.
These are just a few ideas that have helped keep my own family in water in emergencies. I hope they help you.