Before water intake (at baseline), we will make the assumption that the subject is in homeostasis with adequate strength of the plasma osmolarity-decreasing effect of water reabsorption as well as normal plasma and urine osmolarities (isotonic) and urine volume.

Step 1: With water intake, water leaves the plasma and osmolarity decreases (diluted, hypotonic).

Step 2: This is in same direction as the plasma osmolarity-decreasing effect of the water reabsorption. Thus, although the strength of the plasma osmolarity-decreasing effect of water reabsorption was adequate before sweating (at baseline), this strength is now too strong (red) to reverse the decreased plasma osmolarity (diluted, hypotonic) produced by water intake. Control by negative feedback is needed.

Step 3: With the strength of the plasma osmolarity-decreasing effect of the water reabsorption before water intake (at baseline) being too strong (red), the negative feedback decreases (blue) the water reabsorption.

Step 4: With the decrease in water reabsorption, concentrated (hypertonic) solution enters the plasma. This will lead to a reverse in the decreased plasma osmolarity (diluted, hyportonic) produced by water intake, increasing it towards normal (baseline, isotonic) osmolarity. Because diluted (hypotonic) solution leaves the tubule due to reabsorption, the fluid remaining in the tubule has increased osmolarity (diluted, hypotonic). Also, with the decrease in water reabsorption, there is more water remaining in the tubule. Overall, the urine becomes diluted and increases in volume.