I got a call the other day. The customer asked how should I wash my folding bike? Should I wash it down with water? Soap? How often should I wash it? She was going to the beach.
The concern is clear. There are bearings throughout the bike. The hubs, headset, pedals, and bottom bracket all have bearings that don't like water. It is best not to get them wet. Water can be used sparingly on aluminum frames in small quantity ( don't hose it down ).
The accepted solution in the industry is to use furniture polish. Using an costly polish will minimize it's usage ( unlike water ). Additionally one needs to use a rag with furniture polish, to make sure it spreads everywhere evenly. This will keep it away from the delicate bearings.
The next question is how often should I wash the bike? Especially living at the beach, does the salt water require additional washing. This is a personal preference issue. Some people wash their bikes weekly, monthly, some never. Aluminum does not rust like steel, so there is no time requirement. The bigger issue is the cables. The cables can rust inside the housing.
Keeping your bike clean is ideal to minimize problems, however it is not required. I would recommend customers keep all cables lubed ( to minimize the risk of corrosion ). in a corrosive environment, folding bikes love living in carrybags. I've had bags corrode at the zippers, this showed me sacrificing the bag can help minimize risk for the bike bike.
FYI I have lived in the Virgin Islands, Hatteras Island, Bahamas, and Hawaii. I often left my bike outside while living on these islands. I never had an issue with my bikes, however I rode on a daily basis, and that helps minimize corrosion issues. I understand that there would be additional risk if the bike would sit unused.