Place dirt right underneath the crazy currents and it should sort itself out automatically.

If it doesn't, add a source block to the place all the water flows to.

Use World Downloader, a client mod which downloads maps from the server and saves them locally. You need to walk around all the areas that you want to download so that the chunks are grabbed.

This is not a perfect solution, as the forum post details:

Important usage notes:

• You need to open chests while downloading or their contents cannot be saved.
• The mod can only save chunks which are sent by the server as you move around. If you see the chunk while downloading, then it's saved! If you don't move, it will likely only save 10 chunks (160 blocks) in each direction.
• The seed is not saved automatically. You must be op to request the seed with the /seed command. World Downloader will pull the seed automatically from the server response.
• When you click "stop download", wait until the world is saved to disconnect. You will be notified in chat.

If possible, get the admin to send you the world files, or at least the seed. If this is not possible, this is about the best you can do.

With the seed however, and carefully checking all chests, you can get a perfect copy of the world. The only thing to do then is to try and find out what server setup your current admin is using (such as plugins and settings).