Due to various circumstances, you have become endowed with primordial energies originating from the elemental plane of water. Explain the origin of your newly awakened affinity; whether it is a divine blessing, the power of a bloodline, a strange coincidence, a deal with the (proverbial) devil, or some other fifth thing. Is it something you wanted? Did you have to sacrifice something to obtain this power? Has this elemental endowment brought about changes to your appearance or personality? If the source of your endowment isn't from the Elemental Planes, simply change the relevant narrative details to suit your character.

Your save DC for this subclass is 8 + your Constitution Modifier + your proficiency bonus.

Elemental Physique

3rd level martial archetype feature.

Divination reveals your creature type to be both Humanoid and Elemental. You have a base swimming speed of 40 feet and you can breathe underwater. Additionally, when you take acid damage, fire damage, or bludgeoning damage, you can reduce the total damage you take by an amount equal to your fighter level, to a minimum of 0.

Primordial Attacks

3rd level martial archetype feature.

You can effortlessly imbue primordial energy into your unarmed or weapon attacks, coating the surface of your limbs, weapons, or ammunition with a layer of mystic water which allows your attacks to count as magical for the purposes of overcoming resistances and immunities. You can exert a small amount of control over this layer of water, allowing you to freely change the damage type of an attack to become either bludgeoning, piercing, or slashing instead of its normal damage type.

Additionally, your water imbued attacks can douse flames. When fighting fire elementals or creatures with water susceptibility, any damage dice that result in a 1 or 2 can be treated as a 3.

Endowment of Water Advancement Options

Choose one option from the list at 3rd and 10th levels. You can choose two options at 7th and 15th levels.

Aqua Guard

As a bonus action or as a reaction before you take damage, you can create a warding shield of water around yourself. Until the end of your next turn, your AC is increased by 3 and you have resistance to all damage. You can use this ability once per short rest.

Be Like Water

You can use a reaction to redirect an incoming attack to hit an adjacent creature within range of that attack, causing you and that creature to both take half the attack's damage. If it is a ranged attack, the attack can be redirected within a cone aimed in the direction the projectile is flying. You can redirect magical and nonmagical attacks. If there are no nearby creatures, you can still redirect an attack to reduce the damage against yourself by half. This ability can be used a number of times per long rest equal to your Dexterity modifier (minimum of 1).

Starting at 10th level, you redirect the full damage of the attack.

Desiccating Strike

Twice per short rest, you can use an action to make an unarmed or weapon attack that forcefully expels the moisture from a creature, inflicting an additional 1d8 necrotic damage on a hit. A creature hit by this attack must then succeed on a Constitution saving throw or, until the start of your next turn, have disadvantage on attack rolls, saving throws, and ability checks that rely on Strength or Dexterity.

Water elementals, plant type creatures, blood-sucking creatures, and aquatic/amphibious creatures are vulnerable to this damage and have disadvantage on this saving throw. Creatures that do not require moisture or blood aren't affected.

The damage increase at higher levels. At 7th level (2d8), 10th level (3d8), 15th level (4d8), and 18th level (5d8).

Flash Flood

Twice per short rest, you can use a bonus action to call up a wave of water that spreads out from you in a 5 foot radius. A creature hit by this wave must make a Strength saving throw. On a failed save, a creature is pushed past the edge of the wave's radius and knocked prone, taking 1d6 + your Constitution modifier of bludgeoning damage. On a success, a creature is not pushed back or knocked prone and takes half as much damage.

The range and damage increase at higher levels. At 7th level (10 ft., 2d6), 10th level (15 ft., 3d6), 15th level (20 ft., 4d6), and 18th level (25 ft., 5d6).

Mystic Veil

10th level advancement option.

When you are forced to make Wisdom, Intelligence, or Charisma saving throw and before you know the result, you can use a reaction to create an illusory veil of water that suffuses your skin, allowing you to add 1d6 to that saving throw. You can do this even if you have advantage on that saving throw. You can use this ability once per long rest.

Ripples in The Weave

You can perceive the echoes of magic within rivers, ponds, swamps, or even sewers, buckets, or humid climates. Within a range of 90 feet, you are able to identify the presence of spells and magical effects that are tied to water or moisture so long as it is not blocked by 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood or dirt. If it applies, you are able to vaguely estimate its direction and distance, the scale and intensity of the effect, how old it is, or if it is familiar to you. You might also be able to determine whether it is foreign to this plane of existence. This feature functions as blindsight exclusively for the detection of magic. It can manifest in one of many ways, such as a 'visible' aura, a distinct scent, tingling on the skin, a vague spatial sensation, etc.

Water Shield

At the end of a long rest, you can expend your fighter hit dice to create a second skin of high-density water, giving you temporary hit points that last until the start of your next long rest. The number of fighter hit dice you can convert into temporary hit points is equal to your proficiency bonus. For each hit die you choose to expend, you gain temporary hit points equal to your Constitution modifier (minimum of 0).

Your water shield is considered vulnerable to damage from magic that drains moisture. If your water shield takes cold damage, your movement speed is reduced by half until the end of your turn. While your water shield is active, any damage you receive from the following types is reduced by an amount equal to your Constitution modifier: force, necrotic, poison, psychic, radiant, thunder.

Waters of Life

7th level advancement option. (Requirement: Water Shield)

Using a bonus action, you can enchant one of your multi-attacks to drain the moisture of your enemy, dealing an additional 1d4 + 2 necrotic damage and restoring the same amount of your Water Shield's temporary hit points, up to its maximum for that day. This ability can be used number of times per long rest equal to your proficiency bonus.

Water elementals, plant type creatures, blood-sucking creatures, and aquatic/amphibious creatures are considered vulnerable to the damage of this ability. Creatures that do not require moisture or blood aren't affected. 

The damage increases at 10th level (1d6), 15th level (1d8), and 18th level (1d10).

Waters of Retribution

As part of a long rest, you can bless a number of objects equal to your Charisma modifier (minimum of 1). The object must be of a size you can wear or carry. To grant these blessings, you must pray to a deity whom you are a devout follower of and expend 10 silver coins per blessed object. A blessed object becomes wreathed in a thin film of holy water for 8 hours.

A blessed weapon counts as a silvered weapon and its damage type counts as radiant damage in addition to its normal damage type. Gauntlets, hand wraps, boots, improvised weapons, etc., that are blessed gain the same benefits. Ammunition shot from a ranged weapon counts as being blessed. As part of an attack, a creature wielding a blessed object can channel the blessing's power into a single powerful attack, ending the blessing on that object and inflicting an additional 1d8 radiant damage to a creature hit by the attack. If it is a melee attack, the blessing does not end if the attack fails to hit.

If the deity you worship is associated to a particular damage type that is more suitable, you can use that damage type instead. If you are condemned by your deity or the clergy of your deity, you cannot use this ability until they forgive you or until you gain the blessing of a different deity or their clergy.

Additionally, you can create holy water in the same way as a Cleric.

7th Level Advancement

Choose two options from the Endowment of Water Advancement Options.

10th Level Advancement

Choose one option from the Endowment of Water Advancement Options.

15th Level Advancement

Choose two options from the Endowment of Water Advancement Options.

Elemental Progression

18th level martial archetype feature.

Once per Tenday, you can transmute your flesh to become a true water elemental for 1 hour. Once your elemental form ends, you gain three levels of exhaustion. While you are in this form, the following changes occur.

• Your flesh and every nonmagical item you are wearing or carrying becomes water, you are semi-translucent.
• You gain resistance to the following damage types: acid, fire; bludgeoning, piercing, and slashing from magical and nonmagical attacks.
• You gain immunity to poison damage
• You gain immunity to the following conditions: grappled, paralyzed, petrified, poisoned, prone, restrained.
• You can enter a hostile creature's space and stop there. You can move through a space as narrow as 1 inch wide without squeezing.
• If you end your turn in a creature's space, you automatically roll to grapple them. If you succeed, it takes 3d6 bludgeoning damage at the start of each of its turns it remains grappled.
• If you take cold damage, you partially freeze. Reducing your speed by 20 feet until the end of your next turn. If a creature is in your space, you both take the full amount of cold damage.