Water in a dark container is actually better than in a clear or semi-transparent container when dealing with heat and extreme sun. Prohibits bacterial growth. That's why you see the above ground water tanks for off-grid homes, and most of the water tanks for livestock, made of black or dark green. Leave a bit of room for expansion, cycle your water, and when empty rinse with a couple drops of bleach included in your rinse water, along with a thorough visual inspection.
I know off-grid guys who catch all their water from gutter systems on low-pitched roofs in the Chihuahuan desert, in huge above-ground black containers meant specifically for water, and keep it for ages before using it, though often run it through simple purification systems if intended for cooking or consumption, not just washing or livestock.
