Hopefully this will clear up what is OEM and OE. There is also a list of manufacturers that make OEM parts for Porsche, water pumps being one of them.
"OEM Porsche Parts�stands for "Original Equipment Manufacturer". Porsche OEM Parts refers to the company that originally manufactured the product for Porsche. When referring to OEM Porsche parts, OEM designates a replacement part that is made by the manufacturer of the original part from factory. Believe it or not, Porsche does not manufacture and produce many of the parts they use to build their automobiles. Like most carmakers they use outside independent companies to help them design the parts used in your Porsche. Porsche then puts the parts in their own boxes with their logos.
How do these parts become available to companies, like ****************************************, to be sold to the end user? After a certain time frame the actual manufacturers of these Porsche OEM parts are allowed to sell them to other wholesale distributors for resale. This time however they come packaged in a box with the name of the actual manufacturer of the part, not Porsche. Its not an inferior part its just put into a different package. In most cases the part will be identical with the exception of the packaging."
Porsche OEM Parts - Original Equipment Manufacturer, 911, 944, 996, Boxster