And, indeed, there are very few choices out there. Vaude made several waterproof packs in the late 1990s, but has mostly abandoned that effort except for a messenger-style bag called the H2O Proof ($130 U.S.; www.vaude.de).
Why not get waterproof panniers? Ortlieb offers some excellent choices in this category. The Back-Roller Plus ($180 U.S.; www.ortlieb.de) can be used as a backpack with a strap system that makes for a superb bike-commuter piece. And it's totally waterproofI was touring with Ortlieb gear a month ago, and it withstood some real downpours. And I should think the weight of a laptop would be better placed low in a pannier, rather than on your back.
Otherwise, you could always buy a waterproof case for the laptop and stick the whole thing in a regular pack. Pelican makes a waterproof hard case for $105 U.S. (www.pelican.com). Or, get a kayaker's dry bag and put the laptop in that, then the dry bag into your pack. SealLine makes great, totally waterproof bags that shouldn't set you back more than about $25 U.S. (www.cascadedesigns.com/sealline).
Support Outside Online
Our mission to inspire readers to get outside has never been more critical. In recent years, Outside Online has reported on groundbreaking research linking time in nature to improved mental and physical health, and we’ve kept you informed about the unprecedented threats to America’s public lands. Our rigorous coverage helps spark important debates about wellness and travel and adventure, and it provides readers an accessible gateway to new outdoor passions. Time outside is essential—and we can help you make the most of it. Making a financial contribution to Outside Online only takes a few minutes and will ensure we can continue supplying the trailblazing, informative journalism that readers like you depend on. We hope you’ll support us. Thank you.