While nominally working on my Al-Qadim Church game (I was also tinkering with some 5e stuff for the Princes of the Apocalypse game I'm playing in and working on a secret project), I've been going through a lot of old and new D&D stuff looking at water spells. My conclusion: no one can write a decent water spell to save their lives.
First problem: what sort of damage does water do? You can't really have a water elementalist without enough water spells, but you also can't really have a water elementalist in 5e without those spells doing damage. The Elemental Evil Player's Companion addresses this a bit by adding some spells that do bludgeoning damage. That makes sense: you conjure a big pile of water and whump someone with it. There was an old water blast in Al-Qadim as well, which is just a big spray of water (generally to the face). Unlike fire, however, there's really only one or two big watery face-blasts you can get away with it seems. Thus far one of my favorites is called Cone of Teeth from 2nd edition, where your watery blast takes the form of shark's teeth and rends your enemies.
Second problem: If you're not conjuring water, you're restricted to natural bodies of water. So many spells involve letting things normally on land bypass or function under water. Maybe you need to float or swim or breathe or see in the water? There's a spell for that, and a water elementalist can surely cast it. Possibly a couple different versions of it.
Third problem: Mist/fog is water, but its also air. A lot of the fog spells are listed as both air and water, and its easy to see why. Rain and weather are a combo of the two elements. So, for better or for worse, air and water need to share some spells or you have to decide to try to limit your possibly spells by restricting things to one or the other element. Related: does waterbreathing fall under air or water, or should there be a distinction between water breathing and lasting breath spells?
Fourth problem: ships are both air and water, but also neither. Ship spells are another issue all together. A lot of water spells are found in ship/pirate type games and supplements because it makes sense that they'd be useful in the setting. But is a spell to conjure rigging really a water spell? What about one that strengthens or weakens a ship's hull? Some of the ship spells are even nonsensical if you consider a water-wizard or water-sorcerer to be a "sea" type. Sea things often include storms and ships, by why the heck would a storm-sorcerer have the power to weaken a hull or conjure rigging with their innate magic? Why would a sea wizard gain any benefit for casting those spells which seem like tangentally related spells?
Fifth problem: Ice. Ice is the easy way out. Sure it makes a little sense since water is actually ice, but not when a water elementalist's primary means of attack is doing cold damage with a frostbite spell or a cone of cold. I certainly don't think a pirate in an Arabian Adventure (or, honestly, pirates in general) should be using Ice Knife and Snilloc's Snowball Swarm as their primary offensive spells till they hit 5th level. Ice sure can make for a nicely thematic set of spells though, especially if you add in wind/weather (and maybe some enchantments and northern lights type spells).
Sixth problem: Conjuration or Transmutation (or Evocation)? Related to the second problem, you can easily make many a water spell a conjuration and then you have no ridiculous need to cast it in/near a body of water. This could be the case with so many spells that it blurs the artifical lines between the codified 8 schools of magic in D&D. In 5e I can really see why they remove a lot of those sorts of limits in spells so tidal wave and wall of water don't need to rely on the surrounding environment. Still, if the schools weren't such a big thing it might be nice for them to get a boost in power when cast in the right environment.
So, what's the verdict? Its hard to concoct some original water spells. I bet everyone could come up with about a 6-12 fairly distinct ones (depending on the granularity) but everyone will basically cover the same ground with their water spells (stay dry, go underwater, get over the water, blast of water, something ice, something fog, manipulate the current/flow...). So I'm left with a few different feelings on this. One can either stretch the definitions of water a bit (and if you do that, why not add in a scalding steam spell alongside a bit of ice and fog), or accept the fact that if a player wants a water elementalist its part of the DM's job to ensure the setting supports water (i.e. ships or rivers will be involved). The latter is a bit unsatisfying, so maybe there's a few more ways one can make spells which are thematically watery (a spell that smooths and polishes objects, or alternately bloats and cracks them; scrying in a pool of water) that can be used to expand the list a bit.
Side note: all the elements are a bit repetitive, but somehow air, earth, and fire ones don't seem quite as bad.
First problem: what sort of damage does water do? You can't really have a water elementalist without enough water spells, but you also can't really have a water elementalist in 5e without those spells doing damage. The Elemental Evil Player's Companion addresses this a bit by adding some spells that do bludgeoning damage. That makes sense: you conjure a big pile of water and whump someone with it. There was an old water blast in Al-Qadim as well, which is just a big spray of water (generally to the face). Unlike fire, however, there's really only one or two big watery face-blasts you can get away with it seems. Thus far one of my favorites is called Cone of Teeth from 2nd edition, where your watery blast takes the form of shark's teeth and rends your enemies.
Second problem: If you're not conjuring water, you're restricted to natural bodies of water. So many spells involve letting things normally on land bypass or function under water. Maybe you need to float or swim or breathe or see in the water? There's a spell for that, and a water elementalist can surely cast it. Possibly a couple different versions of it.
Third problem: Mist/fog is water, but its also air. A lot of the fog spells are listed as both air and water, and its easy to see why. Rain and weather are a combo of the two elements. So, for better or for worse, air and water need to share some spells or you have to decide to try to limit your possibly spells by restricting things to one or the other element. Related: does waterbreathing fall under air or water, or should there be a distinction between water breathing and lasting breath spells?
Fourth problem: ships are both air and water, but also neither. Ship spells are another issue all together. A lot of water spells are found in ship/pirate type games and supplements because it makes sense that they'd be useful in the setting. But is a spell to conjure rigging really a water spell? What about one that strengthens or weakens a ship's hull? Some of the ship spells are even nonsensical if you consider a water-wizard or water-sorcerer to be a "sea" type. Sea things often include storms and ships, by why the heck would a storm-sorcerer have the power to weaken a hull or conjure rigging with their innate magic? Why would a sea wizard gain any benefit for casting those spells which seem like tangentally related spells?
Fifth problem: Ice. Ice is the easy way out. Sure it makes a little sense since water is actually ice, but not when a water elementalist's primary means of attack is doing cold damage with a frostbite spell or a cone of cold. I certainly don't think a pirate in an Arabian Adventure (or, honestly, pirates in general) should be using Ice Knife and Snilloc's Snowball Swarm as their primary offensive spells till they hit 5th level. Ice sure can make for a nicely thematic set of spells though, especially if you add in wind/weather (and maybe some enchantments and northern lights type spells).
Sixth problem: Conjuration or Transmutation (or Evocation)? Related to the second problem, you can easily make many a water spell a conjuration and then you have no ridiculous need to cast it in/near a body of water. This could be the case with so many spells that it blurs the artifical lines between the codified 8 schools of magic in D&D. In 5e I can really see why they remove a lot of those sorts of limits in spells so tidal wave and wall of water don't need to rely on the surrounding environment. Still, if the schools weren't such a big thing it might be nice for them to get a boost in power when cast in the right environment.
So, what's the verdict? Its hard to concoct some original water spells. I bet everyone could come up with about a 6-12 fairly distinct ones (depending on the granularity) but everyone will basically cover the same ground with their water spells (stay dry, go underwater, get over the water, blast of water, something ice, something fog, manipulate the current/flow...). So I'm left with a few different feelings on this. One can either stretch the definitions of water a bit (and if you do that, why not add in a scalding steam spell alongside a bit of ice and fog), or accept the fact that if a player wants a water elementalist its part of the DM's job to ensure the setting supports water (i.e. ships or rivers will be involved). The latter is a bit unsatisfying, so maybe there's a few more ways one can make spells which are thematically watery (a spell that smooths and polishes objects, or alternately bloats and cracks them; scrying in a pool of water) that can be used to expand the list a bit.
Side note: all the elements are a bit repetitive, but somehow air, earth, and fire ones don't seem quite as bad.