

Yeah, you’re not supposed to use it when you’re fully congested because the water will just get trapped and sit.
There’s a bit of a learning curve and people hesitating can end up with the uncomfortable sensation of “water up your nose” but it really is awesome and life changing once you figure it out.
US, but I don’t know that should matter. Even in France, water comes from a variety of sources and boiling / using distilled water eliminates risk, no matter how small.
In my family’s commune (France), there’s a lot of calcium in the tap water - such that you could actually feel it on your skin and in your hair after a shower, appliances like the coffee maker got crusty deposits with use. My grandmother only drank bottled water, I wouldn’t put that through my sinuses even if it were boiled.