1 For best results from your flask, before use, pre-fill for about 3 minutes, using either hot water for hot drinks or cold water for chilled drinks. 2  Never use a microwave or conventional oven to pre-heat your flask.  If your flask has not been used for some time, rinse with warm water to remove any residual odours.
2. : the degree to which something is prevalent; especially: the percentage of a population that is affected with a particular disease at a given time.
Prevalence means there is a lot of something. If you get a bad grade on a paper for having a prevalence of typos, you need to proofread your work more carefully. The word prevalence comes from the Latin praevalere, meaning condition of being widespread or general.. The word is often used to describe a phenomenon that is widespread in a community, like the prevalence of a disease across a country.