Your dream about the waterpark could symbolize various aspects of your life, particularly those related to family dynamics, exploration, and perhaps feelings of being overwhelmed. Here are some insights into different elements of your dream:

1. Waterpark: Water often represents emotions and the subconscious. A waterpark, with its playful and chaotic environment, may indicate a desire for fun and relaxation, or it might reflect feelings of being overwhelmed by emotions or responsibilities.
2. Getting Wet: The necessity of getting wet to access your room could symbolize the idea that you must confront or embrace your emotions to find comfort or security in your life. It may suggest that you need to deal with certain feelings before you can find a sense of peace.
3. Expansion of the Resort: The waterpark becoming bigger could represent personal growth or the feeling that your life is becoming more complex. It might indicate new opportunities or challenges that are emerging in your life, and how you're navigating them.
4. The Gate: The small, faded yellow gate might symbolize boundaries or obstacles in your life. Since you feel you've seen it before, it could represent a recurring issue or a part of your subconscious that you're trying to understand. It might be an invitation to explore what this gate represents in your waking life.
5. Your Brother: The presence of your little brother and his playful act of dumping water on you could symbolize familial relationships and the dynamics within your family. It may suggest that you feel a sense of responsibility for your siblings or that they play a significant role in your emotional landscape.
6. The Call to Return: Your brother’s message about your dad looking for you might indicate a need to reconnect with family or to address responsibilities that you may feel are being neglected.

Overall, this dream seems to reflect a mix of fun and complexity in your life, highlighting your relationships with family and your emotional state. It may be helpful to consider if there are any current situations in your life where you feel overwhelmed or if there are emotions you need to address. Reflecting on these themes might provide clarity and direction in your waking life.