How to measure total energy usage of an arduino board
In order to calculate the amount of energy you have to calculate the power first.

The relation is 

Energy = (Power * Time of usage)

How to calculate the power?

The voltage for each device in the system is constant. What changes is the current withdrawal in each component in the project.
The main thing you have here is the pump and how much does it consume current.
Usually, you will have on the "plate" of the pump the current withdrawal of it.

Say it consumes 2 Amps.
If that is not available there, use a DMM "Digital Multimeter" and connect in series with the pump and measure the amount of current.

If there are any other major/important components in your project just calculate the current withdrawal from them.

Now add up all the currents and say you ended up with 2 Amps.

If all the components are operating at the same voltage, just multiply the total amount of current withdrawal by the voltage.
WHY?
Because:
P(power) = V(voltage)   * I(current)

If not, just find the power of each component.
Add up all the powers of all you components.

Now you will only have to calculate the energy.

E(Energy) = Power * time

Time here refers to how long is your system working?
Is it a full day, couple of hours. IT doesn't matter. Usually to make things easier use time (in terms of hours).

Say your power ended up with 3kW kilo Watt
You've run the system for 2 hours every day
Energy = 3 * 2 = 6 kWh

If you've kept this for a full month.
Energy save in a month = 180kWh.

Just find out how much do the ministry cost for each kWh, and you'll know how much money you've saved!