There are all sorts of reasons to keep your vehicle in good repair and well maintained. A well maintained vehicle is safer to drive and more likely to stay under your control. It is less likely to quit at a critical time and leave you stranded. It is more likely to be ready to go when the getting is good and to be able to haul you and yours out of trouble.

It is also less likely to make you sick.
http://scienceblogs.com/thepumphandle/2010/06/legionnaires_disease_linked_wi.php

This is also one of those stories that makes everyone a little bit paranoid. The revelation that your vehicle can make you sick in subtle ways, ways you might not have expected, should remind everyone that we are all vulnerable. That no matter how hard you try there is something you haven't planned for. That while everyone here might run out and refresh their windshield washer tank there are always going to be things we have overlooked.

Keep well and maintain your vehicles. They may save your life. And certainly make life easier. But be aware that you can't know it all, or do it all. That safety is mostly a matter of statistics. That you can shift odds in your favor but you're never going to be absolutely safe. There are always going to be hidden hazards. Like legionnaires from you windshield washer tank. Who knew?