CONSULTANTS.

They also regulate the volume of water in the body by producing urine that is either more concentrated than blood (deep yellow urine) or more dilute than blood (a clear urine that looks like water). More than 99 percent of the water filtered from blood by the kidneys is reabsorbed in the kidney tubules, allowing excretion of nitrogenous waste products at a 100-fold-or-greater concentration in urine as compared to blood. If urine concentration increases to a normal value, then it is likely that your horse has psychogenic polydipsia, which means he drinks excessive amounts of water. To regulate the volume of water in the body, they produce urine that is either more concentrated than blood (deep yellow urine) or more dilute than blood (a clear urine that looks like water). [Extracted from the article]