Discuss plans with a local business consultant to find out whether it is feasible to build a water park in your area or not. You should choose a consultant who should be able to figure out the initial cost and potential return for a period of 10 years.
Organize a local gathering of people in your town and discuss with them your plan to build a water park in the area. Invite influential people, important government officials, and seek out their opinion about the project. Do not discuss anything related to the design and size of the water park, this meet up is meant for the purpose of finding the response of the community to the project.
If you get positive response from the community, start researching on your project. Visit at least 5 major water parks and finalize the design of your park.
Decide the piece of land where you want to build your water park. After finalizing the choice of land, you should be able to estimate the total cost of the project. Hire the services of a finance guy to estimate the approximate cost of the project.
Figure out how you intend to finance the project. There are plenty of options to decide from. You can get a loan from a bank but they come with pretty high rates of interest. An alternate is to get the project the financed by a single or a group of investors, but for that you will have to get their trust first.
Throw a party for the influential people of the community and discuss your plan to build the water park. Get their interest from a business point of view, and ask them to invest in the project.
Plan the layout of the project. When the start up money has been transferred to the prime account, start building the water park right away.