1 In general, the total dissolved solids concentration is the sum of the cations (positively charged) and anions (negatively charged) ions in the water.  Parts per Million (ppm) is the weight-to-weight ratio of any ion to water.
If you refrigerate the rice, and you want to eat it cold, its perfectly fine. People eat cold rice salads all the time. Cold rice pudding is fine. Its just sitting around at room temperature that is the problem.
It depends on the individual. In the past, most Japanese ate rice three times a day. These days, they're eating it less often. Rice still is Japanese staple food. But many of them now eat a western breakfast - toast and eggs instead of rice, fish, and pickles. And they might eat noodles for lunch instead of rice. But most people still eat rice with dinner every night.