Scorpio is the deep water
Scorpio is the DEEP water, it is the subliminal, subconscious waters. This water is primal. Scorpios are in touch with the most primal of emotions. Although they may feel their feelings, it can take time to understand them as they surface. This is because they rise from such depth, from a subconscious, primal undifferentiated place.
It is said that Scorpios holds the shadow material of our culture, this is serious business because we know there is a lot of that going around! The Scorpio Sun needs to dive down into the depth of the water, to discover their inner truth in order to come up and shine. It is this deep exploration, akin to an alchemical process, which makes a Scorpio Sun shine.
Pisces are the collective water, think of the open ocean, it is vast, without boundaries. Cancer is the personal water, it is specific to you. The stream outside your house or even your bathtub. Cancers are focused on their personal feelings and their internal world.