In the newly diagnosed diabetic dog or cat, it is common practice for the veterinary staff to instruct the owner how to draw up and administer the insulin injection to their dog or cat.
In most cases, we have the client practice the subcutaneous injections with sterile water or saline rather than the insulin solution itself. This allows the client to practice giving an injection multiple times if needed. Obviously, we can't give multiple insulin injections within a 15-minute training period!
If this is done, I've found that it is better to use saline, Lactated Ringer's, or another balanced fluid solution rather than sterile water for this purpose.
The subcutaneous administration of sterile water can be quite painful for the pet. If the dog or cat reacts adversely to the practice injection, that can make it more difficult for the owners to administer insulin at home. We all know that administration of any of the commercial insulin solutions, especially with today's small gauge insulin needles, are essentially pain-free!
Remember that many of our pet owners are really afraid of giving injections. Some may even consider euthanasia if their pet has developed diabetes. The last thing we want to do if have them believe that the insulin injections are going to be painful for their pet.