If all Devil Fruit users in One Piece anime are not capable of swimming, what about a Devil Fruit user whose ability is to control water? Can such a person able to swim or evade the Devil Fruit's curse?
Most of this answer is speculation as there is currently no answer to this question.
I think that the possibility of the "Mizu Mizu no Mi" existing somewhere in the One Piece universe is highly possible, since we have already seen multiple states of water being Devil Fruits:
- Moku Moku no Mi (Smoke - Gas state)*
- Hie Hie no Mi (Ice - Solid state)
- Yuki Yuki no Mi (Snow - Solid state)
* I know this one is disputable
The only problem with the "Mizu Mizu no Mi" is that it will create a paradox. Since Devil Fruit users are weak to water, if a Devil Fruit user transforms into water, he would be rendered powerless and transform back to his normal form.
But all in all, I don't think the person using this Devil Fruit will be able to circumvent the "curse" Devil Fruit users get from eating them.
The thing is that the Devil Fruit users only lose their powers through SEA water. drinking water, fresh water and any other type of water would have no effect. So it would be possible to have the ability and swim, if you are not in Sea water. This was displayed in the Crocodile ARC. Luffy dowses himself with regular water to fight Crocodile for the fact that the Sand gets clumpy and is not able to disperse.
TL;DR YES, they can swim
Assuming the fruit eater cannot control the sea water (which otherwise would clearly goes against all the plot), he'd have to use tricks to enable him swimming.
Devil Fruit users are susceptible to all types of water, not just seawater
I'll assume this Devil Fruit will not be susceptible to fresh water. This can be possible since the wiki always states the word "sea" as the weakness. It has nothing to do with water. For example, it's "seastone", not "waterstone". We can say susceptibility of fresh water is a side effect which can be neutralized with the power of the fruit.
Logia Devil Fruits allow a person to create, control, and transform into a natural element or force of nature, depending on the fruit.
Let us also assume the fruit is Logia type. If the fruit has the ability to create water, the fruit user could surround themself with newly created fresh water which is not their own body. This way, there will be no direct interaction with the sea water and the Devil Fruit user.
With these assumptions, yes, a fruit user with such power will have the ability to swim in salty water.
Check this answer for further details.