I have a "thing" about sports lids, the kind you can pop up and down. I like/love those. Plasticy rubbery straws and reusable plastic bottles give me the ick. As do plastic cups, especially reusable ones. Plastic one use bottles are ok - and for years I reused them for months until my dad kept telling me off about the chemicals leeching put of them.
Mugs are wrong, glasses are obviously the best but hard to keep water level reached when being busy all day (I'm meant to medically aim for over 3 litres a day)
Anyway long winded way to say I dont find water from a metal bottle tastes any different and it stays so delicious as I put it in from a large glass bottle (of tap water) stored in the fridge. I looked hard to find a metal bottle with a sports lid (I love these as it makes it easy to drink large volumes even if you feel a bit bokey - I think the water hits your throat at a different angle)
So my recommendation is Chilleys 500ml flask with a sports lid. I bought mine as a normal flask and added the lid as an extra as I wanted a nice design on mine, so i also have the option of a screw on lid and using it for hot drinks. DH just got their sports bottle.
I'm also going to take this opportunity to ramble in anger about how most squash now is made with no sugar and such tastes like shite and I no longer drink it. We should not be policed to the stage where we aren't allowed to make decisions over having lovely sugar in cordial rather than having it taken away totally. This is why I love my water bottle so much....I have nothing left to drink, and gin is a bit much 24/7