[Bring_Back_Shantz]

Spoiler!

When it’s 99% water and 100 kg that means you have 1 kg if non-water (let’s say salt)
After the water evaporates you still have 1 kg of salt that is now 2% of the mass (if the water is 98% the salt must me the remaining 2%.
We know the mass of salt so we can use that to figure out the mass of the total.

Total mass = 1 kg/0.2
Total mass = 50kg
1 kg salt
49 kg water