Possible Clues:

• All in the water with the money all in it
• No help if empty on that rainy day — everything inside soaked!
• Pocket case for money and documents
• Barrier against alien - there could be money in it
• Presidential portrait site?
• When it's all in the water there may be money in it (6)
• When the whole of it is in the water there's money in it
• You might open it for a charity
• It's all in the water - along with your liquid assets
• Everything in water when there's money in it