There are several methods of getting drainage plans for your house, you can start of by contacting any of the following entities: Local government planning and building department: They potentially may have information for your property and can provide you with a copy of the plans or direct you to the relevant department or company that can help you. Licensed land surveyor or engineer: These professionals can create a preliminary drainage plan for your property. They will also be able to provide you with any necessary permits or approvals required by government regulation or your local council. Online communities: check out local community groups on social media, or online forums to gain a personal insight from locals who have a similar need as or have already gone through the process. It’s paramount to note that some local councils in New Zealand do not have public records of drainage plans, in this case you may have to hire a private land surveyor or civil engineer to create a drainage plan for you. Before engaging in this project make sure that you are legally allowed to make changes to the drainage system in your area by researching local regulations.