The kidneys work harder when you eat a high salt diet because salt has the ability to dehydrate the body. Salt absorbs water, and when water is absorbed within the body, the kidneys will have a hard time to process the excess salt that is entering in it to be filtered and converted into materials that can be excreted.
The kidneys will not have a hard time to work when you drink a lot of water, in fact it hastens and makes the kidneys more efficient in flushing out excess waste from the body.
