The kidneys are one of those organs that we often take for granted—until there’s a problem. But the kidneys are extremely important, always working in the background to keep us healthy (and, quite frankly, alive) by regulating fluid levels in the body, filtering waste and toxins from the blood, and regulating blood pressure.

But how exactly can you know what kind of shape your kidneys are in? After all, it’s not like you can see them. Here, a nephrologist shares the number one way to know your kidneys are healthy, warning signs that there could be something wrong, and ways to support your kidney health.