The property is not allowed to close the terrace, but it will flow into the water along the lower edge of the sliding door when it rains. Ask an expert to help me. What should I do?

Property has no right to enforce the law. You just need to seal the balcony with glass windows of the same color. The property may not agree with you. This is because laws and regulations can't be sealed, but after you seal it, he can't help it. As long as your balcony is not too abrupt and beautiful, the property will not embarrass you with such a trivial matter. At least you're his master.