75 million Americans are under heat alerts today as the hottest weekend of the year kicks off. The heat wave is threatening about 40 million people’s water supply out west. In the east, Amtrak is warning that trains need to slow down because it’s so hot. Officials reported heat-related deaths in Texas and Pennsylvania, both victims were older with underlying conditions. Heat kills an estimated 1,300 people every year in the U.S., which is more than any other weather event. | NBC Nightly News wit