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.
Incidence is the frequency with which an event occurs within a given time period (such as one year). For example, it could be said that the incidence of new breast cancer cases in 2007 demonstrated 50,000 new cases. By contrast, prevalence refers to how many people currently have that condition this year.