The filtrate is composed of water, ions (sodium, potassium, chloride), glucose and small proteins (less than 30,000 daltons -- a dalton is a unit of molecular weight). The rate of filtration is approximately 125 ml/min or 45 gallons (180 liters) each day.idney Filtration. In the nephron, approximately 20 percent of the blood gets filtered under pressure through the walls of the glomerular capillaries and Bowman's capsule.