It depends on how long you need to store the water for but a few weeks is nothing. Just have the water in a food grade container and make sure nothing contaminates it. If you're going to keep water for months then seal it up to keep dust and other stuff out.
I had 3 tiers stands in my fish room and used the top row of tanks for holding water. I filled them with tap water, dechlorinated and aerated them, then added minerals if I needed to raise the hardness and pH, or peat if I wanted it for breeding blackwater fishes. The water sat in those tanks for a week before I did water changes.
I had a friend who kept Tropheus (African Rift Lake cichlid). He had a couple of 200 litre (50 gallon) plastic wine barrels in his fish room. He filled them with water and added Rift Lake water conditioner to increase the GH
and pH. Aerated it for a week before doing water changes.
Another friend used a 200 litre plastic wheelie bin. He brought it inside the day before he did water changes. filled it with water, dechlorinated and aerated it. The following day the water would have warmed up to room temperature and he did his water changes.
A lot of people with fish rooms have water holding facilities. I knew a guy that had a 20,000 litre rainwater tank for his fish room. Most people don't go to that extreme but many will have containers of water sitting around for a week or two so they have water ready for water changes.