Calcium is found in modest levels in watercress (44 mg per 250 ml or 1 cup serving). It's worth noting, however, that this calcium is bioavailable, meaning that a significant percentage of it may be absorbed and utilised by the body. Watercress has a 67 percent calcium absorption rate, compared to 32 percent for milk and 5 percent for spinach. Because a 250 mL portion of milk provides 315 mg of calcium, it remains the most important source of calcium in the diet. Although milk has three times the amount of useable calcium as watercress, using it in a well-balanced meal is an intriguing method to boost your daily calcium intake.