Waterborn Origin
A Soul Smoothed By The Waves
Almost every world that holds life, holds water.
The two share an innate connection of body,
blood, wave, and flesh that is always present.
Sometimes, this connection flows strongly
enough that a sorcerer is born who can feel
the weighty power of water saturating their
being. The wide seas are colossal engines
of energy, playing host each hour to the
clashing of forces greater than a thousand
city-sized explosions, even as they churn
together the most essential nutrients of life.
Just a tiny rivulet of this power, directed into
a mortal being, is an incredibly potent boon.
As a waterborn sorcerer, perhaps you
come from a long line of those dedicated
to the sea - fishermen, sailors, or lighthouse
keepers. Perhaps the connection inherent
in your blood was awakened in the heart of
a terrifying storm. Whatever your origin,
you owe your power to the worldly movement
of the tides and the flowing of rivers. You have a
seemingly bottomless well of power to pull from, if
you can master the shattering pressures of channeling
such magic through your soul.
Push & Pull
Starting when you choose this origin at 1st level, you gain an innate feel for and control over the flow of magic. Whenever a creature succeeds on its saving throw against one of your sorcerer spells of 5th-level or lower on the turn you cast it, and would otherwise take half damage from the spell, you can use your reaction to pull back the swelling magic before it is fully expended. The spell's effect is cancelled, and you regain the spell slot used to cast it, as if it had never been cast. You can do this a number of times equal to your Charisma modifier (minimum of once). You regain all expended uses when you finish a long rest.
Tidal Blood
Starting at 1st level, you can feel the tug of the moon on your own blood just as it affects the oceans. You always know when it is high or low tide, and you can navigate by sensing the position of the moon or similar orbital bodies. While concentrating on this sense as if concentrating on a spell, you cannot become lost except by magical means.
In addition, you can communicate simple ideas with beasts that can breathe water. They can understand the meaning of your words, though you have no special ability to understand them in return.
Changelog
Image credit Titus Lunter - 'Jaceic' Island
Ocean Affinity
At 6th level, you gain the ability to breathe underwater and a swim speed equal to your walking speed. While immersed in water for at least one minute, you gain temporary hit points equal to your sorcerer level. If you spend a continuous hour immersed in water, you gain these temporary hit points again at the beginning of the next hour, and at the beginning of each subsequent hour spent immersed.
Arcane Flood
Starting at 14th level, you can release your magic with the overwhelming power of surging waters. When you cast a sorcerer spell of 1st-level or higher, you can expend 5 sorcery points as a bonus action to open the floodgates to your full might. For 1 minute, or until you are incapacitated, your sorceror spells overcome any damage resistances and cancel any sources of advantage on saves against them.
When your floodgates close again, you suffer one level of exhaustion.
Fathomless Power
At 18th level, you can draw up energy from the depths of wordly magic to sustain yourself. As an action, roll a d12 and add your Charisma modifier. You immediately regain a number of sorcery points and hit points equal to the roll, up to your respective maximums.
Once you use this ability, you must finish a long rest before you can do so again.