I know if you eat too much sodium you retain water, and potassium is similar to it, so I was wondering if it had any effects of that sort on the body.

I bought a new water softener for my new house. I was told by the installer to only use potassium chloride and not salt. He said that salt will ruin the pipes. Is this true? Can I use salt? The reason I ask is because where I live the potassium chloride costs about 3 times as much as the salt.