No Salt Softener Water Treatment. Alternative to Water Softener. What do Aqua-Rex Physical Water Conditioners do? Prevents calcium sticking to surfaces. Cleans out existing scale. Partially softens hot water. Aqua-Rex is an advanced electronic device that has been used for the treatment of hard water in the UK and the rest of the world since 1993. It is widely used in homes, schools, offices, factories and hotels with many hundreds of thousands installed and successfully working. Aqua-Rex is also the only device of its type to have been scientifically tested to prove that it can deliver partially softened hot water.