[neilep (OP)]

Sometimes, when I open a bottle of still water I get a pffffffffffft sound ....just like when opening a fizzy bottle....


why is this and what has happened to make it happen !!

[Karen W.]

Just air escaping I would think!

[neilep (OP)]

Just air escaping I would think!

Thank you Karen...but if I fill a bottle and then immediately open it...there is no pfffffffffft !!..this happens after a time.....so...somehow a gas must generate !!

[Karen W.]

I never thought about that what about heat and cold expansion etc can that build up pressure? Does water expand in a bottle when heated because it can't escape like it would normally when heated.. and evaporation starts taking place?

[Karen W.]

Maybe building pressure instead of evaporating?

[Karen W.]

Or wait when you fill the bottle you create air bubbles then you cap it and the water settles, the bubbles surface the air is released, and then perhaps cause the pressure pop! MAYBE?? You know I am only guessing.. what do you think?

[another_someone]

I never thought about that what about heat and cold expansion etc can that build up pressure? Does water expand in a bottle when heated because it can't escape like it would normally when heated.. and evaporation starts taking place?

My first though was that this was the most likely explanation, but I now wonder if maybe the bottles aren't pressurised deliberately when they are bottled.  Pressurising the bottle would have two advantages:

• It will keep the throat of the bottle under pressure, and will possibly improve the seal between the bottle and the cap, so reducing the possibility of contamination.
• Positive pressure within the bottle would mean if there was a momentary leak, for any reason, it would force matter out of the bottle rather than sucking matter in, so again reduce the likelihood of contamination.

[Karen W.]

I think Neil might mean even water he fills up with tap water does this? Is that right Neil, or do you mean pre purchased water?