A list of low tech inventions over the last few decades that have changed the world. I didn't realize oral rehydration salts were a relatively recent invention:
By the early 1990s, diarrheal diseases were killing some 5 million children under the age of five every year. That number is down to about 1.5 million, thanks to oral rehydration salts—a mixture of salt and sugar that can be dissolved in water and administered at home. Zinc is sometimes added to the mix to reduce the severity and duration of diarrhea. This simple innovation has perhaps saved more lives at lower cost than any other.