I refill the single-use plastic water bottles dozens of times. Cannot be accused of littering.
I'm far more interested in my travel and the environment than which bottle my water is in.
Common to fill half a dozen of those for even a day trip.
They don't leak. Even in the house, I have re-used them for months.
In the Snowy Mountains of Australia, I carried a big hard water bottle and a soft, squeezable bottle.
I could use the soft bottle to suck up water from a 1" trickle of a stream to fill the big bottle easily.
We have had serious village water system problems all summer, just got the lift yesterday and the water is OK to drink.
I have 2 x 2 gallon/10 liter plastic water bottles in the back of my Suburban for drink and for washing up, etc.