Decoupling high current load and 5V regulator
One really good way to deal with this is to simply add a diode (eg. 1N4004) in series with the input and increase the 330nF (or parallel it) with something a bit larger such as 1000uF/16V. 

That way you are not trying to supply the surge to the pump, merely to supply the regulator with its input voltage and the capacitor can be much smaller for the same effect.