With this heat wave already causing blackouts in Brooklyn, Queens and Staten Island, my best advice if you experience one is to fill up your bathtub with water right away! I live on the 12th Floor of our apartment building and in the big blackout of 2003 we soon learned that water gets up to the rooftop water tanks using electric pumps. Once this water supply is gone, you're out of luck and then the only option for draining toilets will be bottled water. As for hygiene, I keep a supply of individually-sealed sanitizing wipes (a variety of brands are available at any drugstore), Purell liquid sanitizer, and also full body wipes (I've purchased these at both EMS and LL Bean but can't find them on their web sites) which are like the hand sanitizing wipes only much larger. For more blackout tips see also: You Need A Phone Like This, Best Lantern Ever, My Favorite Flashlight.
7 months ago