A simple way of keeping track of your customer's history is to use either a 3-ring binder with loose leaf paper, 3x5 index cards, a PDA device, or computer database.
For each separate customer, you want their name, address, telephone numbers, and email address. Below that info, indicate if they are a service agreement customer or not.

Keep track of each date you visited, your invoice number, and a brief summary of what you did. Note their water pressure, and time of day you tested it.

If you made any recommendations, make a note of that as well...so you'll have something to talk about when you do your follow-up.

As you start building your clientele, update the file after every visit.

When Mrs. Smith calls back 3 months later for something unrelated to what you've already observed, you can ease her back into your recommendations.

In Use
“Mrs. Smith, do you recall during my last visit that I pointed out your widget was showing signs of failure?”
Whether Mrs. Smith says yes or no, reply with the following.
“Would it be alright if I took another look at it today after I take care of your other widget?”
If she starts to resist you, or asks why you want to look at it, say the following.
“Mrs. Smith, I keep records of my customer's plumbing details, and want to be sure that I've got all the details right.”
After you've finished fixing the widget, go to the recommendation widget, re-verify that it still needs repair/replacing, and make another attempt to close on the additional task.