Need large food grade water container

[ferret]

I won't store the ro water at exterior particularly the area underneath sunlight.
You need to consider if there is any possible speed growth of unwanted algae even you've a powerhead circulating the prepared water. The rapid changes of outdoor temperature is also a factor need to be considerated. Moreover, I'll use all the new ro water within a week rather than storing the water for more than 8 days. HTH