Leakages and Injections
Leakages: A leakage is any "income recieved within the circular folw that does not flow directly back". (1) An example of a leakage would be savings because savings is the portion of income that is not flowing directly back into the circular flow model.

Injections: An injection is "any spending flow that is not dependant on the current level of income". (2) An example of and injection would be investment spending.

Endnotes:
(1) John E. Sayre, Allan J. Morris, Principles of MacroEconomics, 6th Edition, (McGraw-Hill Ryerson, 2009), Page 92.

(2) John E. Sayre, Allan J. Morris, Principles of MacroEconomics, 6th Edition, (McGraw-Hill Ryerson, 2009), Page 93.

other leakages include
  • taxes
  • import spending

Other injections include
  • government spending
  • export spending

If economy is steady:
Y = C + I + G + (X - Im)
Leakages = Injections
S + T + Im = I + G + X

Net export = X - Im


REFERENCE:
Dr. Stephanie Powers, "Circular Flow"(Lecture, Donald School of Business, Red Deer AB, Winter 2012)