It cannot drown....

In order to drown you need to be a creature that breaths...This creature does not have lungs, and thus does not breath. Thus, it cannot drown. nor can any elemental.

OMG, so wait...if you were to say...get proficiency in athletics AND expertise in athletics as a druid...it would carry over to your wildshape.

Relevant sections of "Wild Shape"
"You also retain all of your skill and saving throw proficiencies, in addition to gaining those of the creature."

AND

"You retain the benefit of any features from your class, race, or other source and can use them if the new form is physically capable of doing so."
Since no anatomy is required to be expert in athletics..you retain the ability.

THUS...the new DC for any grapple check would be 10+str+prof+prof (expertise)...for the water elemental, this would be 10+4+6 for a DC of 20! HOLY CRAP.

I let one of my players use this monster in an encounter against the other players after they let him die. He used it to go strait up their asses.

Quote from TenezLeDroit >>

It cannot drown....

In order to drown you need to be a creature that breaths...This creature does not have lungs, and thus does not breath. Thus, it cannot drown. nor can any elemental.

Do you have any kind of citation for this? Creatures that don't need to breathe, or can breathe water, usually so say somewhere in either their stat block or the description below it; see Adult Black Dragon or Zombie.

While a water elemental might look like living water, it isn't water at all, it's a creature, and presumably still needs various things in order to survive. In the absence of a rule saying it doesn't need to breathe (or can hold its breath for prolonged periods) that seems to mean that oxygen is one of those things, and it could die without it following the normal rules for suffocation.

Although it does seem weird for it to have no advantage to water breathing at all, unless I've completely missed something the only bonus they have is their high Constitution. But I suppose if they normally exist and hunt on the surface of the water, or along the coast or the edge of lakes etc. then maybe they don't usually need to breathe underwater in the first place?

Does this creature do normal bludgeoning damage or magical bludgeoning damage ?

Can the "Freeze" ability trigger multiple times if it takes multiple sources of cold damage, reducing its speed to 0?

. 

Quote from Mr_Maggot >>

A raging tempest, if you will

 Or a Disney princess. 

...If you cast Command on a Water Elemental and tell it to "Freeze" (I have a Paladin who's a former City Guard) would they stop moving or freeze solid?

Quote from Gauntletblade >>

...If you cast Command on a Water Elemental and tell it to "Freeze" (I have a Paladin who's a former City Guard) would they stop moving or freeze solid?

 stoping moving would be the sensible option, but you could rule that the water elemental has perfect control over the entirety of its form, thus being able to arrange its atoms in a crystalline structure and ceasing their movment. mechanically this'd petrify them for a round

Are Elementals made of the element they represent?  Is this creature made of water?  If so can you cast destroy water at a high enough level to instant kill this creatue? 

So how does a druid as a water elemental or an elemental on its own drown someone that it has grappled? Do you just follow these rules?

Drowning in 5E takes the same rules as standard suffocation. A creature may hold its breath for a number of minutes equal to 1 + Constitution Modifier (minimum 30 seconds). After you run out of breath, you survive for a number of rounds equal to Con Modifier (minimum 1). At the next turn, you drop to 0 hit points and are dying. You can’t stabilize or heal until you can breathe again.

How long would someone have to be held in the water until they are past the point of being stabilized or healed?

As for the drowning, you can hold your breath a number of minutes equal to 1+Con, but to me that would apply if you're expecting to be underwater, like diving in. In a combat situation like being hit with Whelm, I'd personally rule that you wouldn't have time to take in a full breath, and would go straight to the second step. After Con rounds you start dying. Otherwise there would basically never be any risk of drowning in a combat scenario.

Once you're at 0 and dying I'd say the normal unconscious rules would apply, and you start making death saving throws. The only difference would be that healing spells don't stabilize you unless you're out of the water first.

Trying to wrap my head around the fact that a water weird is invisible in water, but a water elemental is only "nearly invisible," and that description is just from the fluff text...

If you dye it red and give it a +1 to ac because of glass armor its the koolaid man

yeah, why does it not say resistant to fire damage

I would say yes because its moving

Quote from OfficeDeldro >>

Why can't the Water Elemental breathe under water

 It doesn’t say it can or can’t but I’d assume it can.

dose it instantly die if somone uses dispel magic on it

Hit it with ray of frost. Walking speed 0 ft.