ordinary plastic water bottles travel well. just make sure they are full to the brim. then wrap in plastic and a towel. a thermos flask might break. an alternative could be a purpose-made water canteen.

pam

stainless steel/aluminium water flasks are probably your best bet, widely available in sports/outdoor shops.

I have a couple I use when out walking, never had them leak.

"Question: Will they confiscate it at the airport even if it's checked in thinking it may look like a bomb?"

Don't worry, it won't look like a bomb, it will look like a bottle of water, lacking all the other bits needed to resemble a device. It might trigger the level 1 automated machine (the first layer of hold baggage screening), but even then a human operator will review the image and clear it.

UncleGus's idea of aluminium bottles is the most secure option but comes with a price tag, Pam's plastic bottles would be good enough for me.

"If they are suspicious when they scan it they will simply open the bag"

Not outside the US they won't. Most airports will use a couple more screening methodologies and if they were still unsure they will reconcile the bag with the passenger and ask them to clarify what it is that they have. Only the TSA goes opening people's suitcase locks, which is a dubious process anyway if you have suspicions about a bag.

I got my water flask at Mountain warehouse,I think the 1litre one was about £4or£5 and the smaller 500ml one was free along with it.

Walmart and Trader Joes will have something similar in the US probably cheaper than a thermos flask.

You are all such savvy travelers and great advice-givers. THANK YOU. Fortunately there are a SuperWalmart and Trader Joe's near me. I will check them out in a few hours when they open. Thank you to all. You have been all so great.

BTW, which one of these do you recommend? Not sure I can find these in the US though?

mountainwarehouse.com/camping/…

Mine are like the ones with the Karibeners on them, well exaclty like them except in shiny Blue and Red like the ones with the scrwe onspout.

I have to question one small part of Pam's otherwise excellent advice.

Liquids expand in low pressure and liquids in baggage in the hold may do so if the baggage hold is not fully pressurised. (You can probably check with the airline about this)

If the hold is not fully pressurised and you use plastic bottles, only fill the bottles to within a couple of inches of the top, squeeze the bottle until the water reaches the top, then put the cap on it. This gives the water room to expand.

that seems to make sense. however, i have found that bottles with a head space arrive at the destination 'sucked in'. and i have had partly used shampoos and so on leak, even when they have been squeezed. so i'm not too sure...

felycrespo, any store that carries hiking gear will have these water flasks. Stores like REI, Eddie Bauer, etc., even WalMart & Target will have some type of them in the sporting goods section. Mail order places like CampMor will also carry them. Just make sure they have a screw-on cap like the ones unclegus showed, not a pop-up drinking spout (which will probably leak).