Any container can be used for water for cleaning brushes. Make sure your container is filled with water as high as you can fill it without spilling. Why? Often, a painter is in a hurry putting this and that color on the paper. If the brush isn’t totally clean because you’ve not managed to fully dunk it in the water container, some residue paint will still be on it when you go to your next color and then voila! Your color intentions are not what you think they should be – you’ll be putting down 2 colors instead of one!
Also, an extra container of clean water is helpful if you need to do clean washes on the paper. It just saves an extra trip to the sink.