Need a component to connect a 9v water pump
Yes, a MOSFET should work just fine. As others have said in the comments, you just need to make sure that it's rated for your desired voltage and current, and that it's threshold voltage is low enough (around 2.5V) that the Arduino is able to drive it to saturation with a logic level 1 (5V).

I've used this one (rated at 60V and 30A) in various projects:

https://www.sparkfun.com/products/10213