Bottled water is  not only expensive but is harmful to the environment. Therefore, I try to reuse the same bottle while traveling. I used to carry a hard-plastic bottle while traveling and then one day at an airport, I saw another traveler carrying a flexible bottle, it looks like a pouch. Compared to a standard 500mL hard plastic round bottle it is slim and hence a good fit for a travel jacket. That’s why I fell in love with one and quickly added it to my traveling gear.

The one I carry around is Big Betty wine bottle. I use it carrying around water and it works perfectly well for urban travel.

Big Betty and a Gatorade bottle
Big Betty (750mL) and a Gatorade bottle (600 mL)

As always, with such items, price varies, so, if you are not in a rush, add a price tracker for it.