well, in the last chapter, i think its 407, oda shows califa taking a bath and nami says something about her losing all her power.
First of all, im pretty sure she didnt bath in salt water
Second, Luffy didn't lose his powers when drinking that fresh water to fight crocodile (i mean he was drenched in water in one part) and didn't lose his powers
Until now, it was held constant that seawater's element makes DF users weak
On the other hand, now its saying that any kind of water makes a DF user weak
That means that DF users will lose their power when drinking water, taking baths, when it rains... its messed up