Every other product; manufactures, shippers and retailers do everything to limit exposure to sunlight and heat.
Cases of bottled water sit outside, next to store windows and hot warehouses. Purchasers leave them outside, hot cars and beds of trucks in direct sunlight.
Even your tap water, exposure to sunlight is kept to zero until it comes out of the faucet (*not Dr Faucet).
That’s to keep stuff from growing in it. Bottled water is too thoroughly dead for that.