How does dehydration affect renal failure?

Usually worsens it: Dehydration leads to less perfusion or bllod flow to the kidneys and can make kidney failure worse.

Can cause it: Severe dehydration can cause +/or worsen kidney failure. Your kidneys are sensitive to the amount of fluid circulating in your body. They are primarily responsible for excreting the extra amount into your urine. Too little fluid going into the kidneys because you are dehydrated keeps them from working well. However, if they have already failed, + you don't make urine, there won't be an effect.