Hi all! I ordered a new engine water pump to have it on hand ('07, 84 k miles) when it's convenient for me to replace the coolant and do the pump at the same time. The water pump was shipped with a desiccant.
A lot of things are shipped with a desiccant. It helps keep moisture from forming in the packaging during shipment.
I'm assuming there are metallic parts that are currently expose and should not be allowed to rust while it sits boxed up in some warehouse. People don't like to buy rusty parts.
Water + oxygen supply = corrosion potential. In use the oxygen initially dissolved in the closed coolant system is quickly depleted. Or, it's not worth the bother for the shipper to figure out which items need desiccant and which don't. Safer/cheaper to put it in all packages.