While leaching o chemicals and microplastics should be of concern, in a quasi-emergency where immediate hydration is advisable, such items in the water is a minor issue (to me, at least).

https://phys.org/news/2018-03-bottled-brands-contaminated-plastic-particles.html

One source in this article states that tap water, in general, is safer than bottled water.

I have a variety of water containers, all filled with tap water, and I imbibe from any of them, without concern, when and if necessary. The water in these containers is only a small fraction of what I generally consume on any given day.

Most of my water is stored in the trunk, which is separated from the passenger compartment. The trunk is considerably cooler than the passenger compartment.

One might consider storing fruits, like apples (something like 85-90% water) if concerned about chemicals and plastics.