I’ve been through 4 of these tops with straws. The only way it leaks is if the little white rubber valve on the top comes off. This has happened to me in my big purse!! What a mess!! But hydroflask doesn’t make a standard size top with a straw so I’ve been getting these.
There is always a risk, however, we have had no problems with this particular model. We also tend to keep the water bottle in the outside pocket for easy access. Our goal is that our child fills the bottle up at least two more times at school. 🙂
When the spout is shut (folded flush with the top) it doesn’t matter if the straw is attached or not. It also would be hard to “bump” the spout from shut to open. I throw it in my purse or gym bag and it has never opened or leaked. Only tip is to mind the valve when cleaning, if that gets dislodged it will leak.