Final answer:
The best practical indicator of salt and water balance is monitoring body weight, as it is a non-invasive method that reflects changes in fluid and salt balance and is easy for ongoing monitoring.
Step-by-step explanation:
The most practical single indicator of salt and water balance in the body is monitoring body weight. This method is non-invasive and can reflect changes in fluid and salt balance. Although measuring plasma sodium and plasma volume provide more specific information regarding electrolyte balance and blood volume respectively, these require laboratory tests which may not be as practical for continuous monitoring. In contrast, changes in body weight can serve as a quick and easily measurable indicator of significant shifts in body water content. Furthermore, while urine color can provide some insights regarding hydration status, it is not as reliable since many factors, such as food intake, medications, and supplements, can affect urine color.
It's important to note that although other methods like urine osmolality tests and concentrating ability tests can provide more detailed insights into kidney function and water balance, the simplicity and immediacy of weighing oneself make it a practical choice for regular monitoring.