I’ve actually done this before, but I only had sodium chloride and potassium chloride. I didn’t think of a Soylent connection at the time (I hadn’t even had Soylent yet, but I’m pretty sure I had seen the original blog post), but I can see why you did.
I googled a bit and the basic idea has been around since at least the 1980s, according to Wikipedia:
Oral rehydration therapy
In 1980 the Bangladeshi nonprofit BRAC essentially developed a door-to-door and person-to-person sales force to teach ORT. A task force of fourteen women, one cook and one male supervisor traveled from village to village, assuming that the women’s numbers would protect them from the supervisor and the supervisor would protect them from others. After visiting with women in the village, each evening they got together and talked about what worked and what did not. They hit upon the method of encouraging the women in the village to making their own oral rehydration fluid. They used available household equipment, starting with a “half a seer” (half a quart) of water and adding a fistful of sugar and a three-finger pinch of salt. Later on, the approach was broadcast over television and radio and a market for oral rehydration salt packets developed. Three decades later, national surveys have found that almost 90% of children with severe diarrhea in Bangladesh are given oral rehydration fluid.
I was also somewhat disappointed to see that I probably have no need for a sports drink unless I’m dehydrated:
Purpose and effectiveness
Athletes actively training and competing, lose water and electrolytes by sweating, and expending energy. However, Robert Robergs, an exercise physiologist at the University of New Mexico who studied Gatorade, said that unless someone is exercising or competing in a sporting event for longer than 90 minutes, there is no reason to drink something with excess sugar and electrolytes. The Australian Institute of Sport states that excessive salt supplementation during exercise may lead to “gastrointestinal problems or cause further impairment of fluid balance” and may cause salt-induced cramps.
Sodium in drinks might help to avoid hyponatraemia (low sodium), but only after sustaining athletic activity for more than four hours; a sports drink containing sodium may be appropriate for recovery from intense and prolonged training or competition.
I don’t remember the last time I did anything besides watch a movie for more than ninety minutes. Forget four hours.