I have always been told to advise patients not to shower with contact lenses in. So why is this allowed with silicone hydrogel lenses?

Secondly, can patients swim in these lenses?

Wearing lenses that have been in contact with any source of water, and as such, any kind of water borne contaminant, is definitely an issue to consider. In situations such as swimming in pools or oceans the risk is great enough to warrant either wearing goggles, or removal and disinfection or disposal after swimming. This is particularly important in places such as rivers and lakes, where the risk of water contamination is even greater.

When showering, the risk, while still present, is greatly reduced. In daily wear mode, as lenses are removed every day, it is easy to completely eliminate this risk, by recommending the removal of lenses before showering. However, in continuous wear, having to remove lenses every day to shower would eliminate the convenience and purpose of extended wear. As such, it is reasonable to choose the convenience of continuous wear over the relatively small risk of domestic water supply contamination.