Method 2 of 8: Cold Saltwater Method (Fresh Blood Stains). 1. Mix 2 teaspoons of salt with 1 cup of cold water. Pour the solution into a spray bottle. 1  Once again, note that it's vital to use cold water because hot or even warm water can set the blood stain permanently to your mattress.. Mix 2 teaspoons of salt with 1 cup of cold water. Pour the solution into a spray bottle. 1  Once again, note that it's vital to use cold water because hot or even warm water can set the blood stain permanently to your mattress.