Of course not. Many such pictures circulate to show how the law has imposed ridiculous requirements on businesses and governments. In reality, such legal urban legends are often based on intentional or idiotic interpretations of tort law and other areas of liability. There is no need to warn for an obvious and open danger like water in a foundation. There is a duty to design such an area with non-slippery surfaces. However, you can taken back the sign and let the water speak for itself.