Keep in mind that a 20L can weighs 20kg, so if you don't have anyone in your household or group capable of lifting that you're going to need to find something smaller that is food safe, opaque and hasn't been used to store anything that isn't food.
It may also be helpful to invest in a funnel for filling them, making sure to have a separate one that isn't used for transferring laundry liquid between containers or anything.
You want to label them with the date you filled them, a pencil on masking tape works fine and won't wash away if it gets wet. Pure clean water in a sealed dark food safe container _shouldn't_ grow anything nasty, but will still start tasting bad over time. I'd recommend storing it in the coldest place you have and rotating it out at least every month.
4/🧵