It's not a theoretical issue, and not limited to RO water supplies. Here in Portland Oregon the municipal water source is Bull Run Watershed high up in the foo

It's not a theoretical issue, and not limited to RO water supplies. Here in Portland Oregon the municipal water source is Bull Run Watershed high up in the foothills of Mt. Hood, some 26 miles east of downtown. The collected water is basically similar to distilled water since it's formed directly from cloud/fog condensate. Consequently the default pH is ~6.8-7.0, which leaches lead from old plumbing. The federal government forced the city to add sodium hydroxide to increase the pH to ~8.0 and reduce corrosion. Obviously city water has very little dissolved solids which in principle could have health implications re: Ca, Mg intake. Diet is normally the main source of these minerals, not clear how much additional risk is attributable to low mineral content of household water. Most people here consider our water to be very palatable as is and are reluctant to have further modifiers applied to it. If any new federal requirements are attempted it's likely to elicit a lot of controversy and pushback.