Liquid and blood are of the same source

When there is excessive loss of blood, fluid seeps into the vessels to compensate for the loss, giving rise to depletion of fluids outside the vessels that manifests in dry mouth, dry pharynx, scant urine, and dry skin. Conversely, loss of fluids as through great vomiting, great diarrhea, or great sweating can cause fluid to seep out of the blood to compensate the loss. For this reason, The Magic Pivot (灵枢 líng shū, běn shén) states, when blood is despoliated, there is no sweat; when sweat is despoliated, there is no blood (夺血者无汗，夺汗者无血 duó xuè zhě wú hàn, duó hàn zhě wú xuè).