I am making an automatic plant watering system using Arduino. My question is that, is a 9V-1A external source goes through Arduino UNO DC Jack enough to power everything (including itself, a 5V moisture sensor, a 5V water pump) simultaneously?
Probably depends how much the pump will draw, and how you have it connected. Do you have link to the data sheet and a schematic?
The sensor likely won't use much, but the data sheet would also be useful.
The amount of current you can get through the Arduino's on-board voltage regulator depends on how much voltage you are "dropping" across it. With 9V in you are only dropping 4V so that's not too bad.
I don't know how much current you can get but the odds are that you can't power a pump.
I wouldn't. The voltage regulator on the Arduino can't handle the water pump in all likelihood unless it's a very small pump like in a cat water fountain but even then no. Just checked: the pump and one LED in my cat's fountain is fed by a USB to wall wart rated at 5v, 1.0A. Highly doubt this would work for you long term, even if you don't damage the Arduino voltage regulator, the sketch will likely reset on you and act up unexpectedly.
A safer way is to always power your motors (which a pump is) separately and tie the grounds all together. Even if you pick off the +9v line of your adapter and regulate it to 5v external of the Arduino you'd be better off I think. It's close though, I mean you MIGHT get away with it.
If that pump is directly connected to the Arduino without a driver, you will blow up your Arduino. The absolute max. output current of a pin is 40 mA, safer value that people use is 20 mA.
Further you need a flyback diode.
Definitely shouldn't drive the motor direct from the Arduino GPIO pin.
You may get away with driving via the 5v rail, but better to drive the motor with another power source. Either way, the GPIO pin should just be used to switch on/off (using a relay or transistor circuit).
Thank you all for the response, very informative, I can't appreciate enough for how responsive you guys are. Thank you all again, what a great community.
Totally useless!
Use a 5 V supply because that is the voltage just about everything requires (though pumps generally require higher). Connect it to the "5V" pin and all other devices requiring 5 V. Just disconnect the "5V" pin while connected to a PC via USB.
You need a FET to control the pump. Look for a "logic-level" FET such as a IRLZ44.