Reverse osmosis filters will already be more common in some places that have harder water (and decided that softening it at the municipal level wouldn’t be cost-effective). If there was fine grained data available about water hardness and obesity levels, that might provide at least a little signal.
Reverse osmosis filters will already be more common in some places that have harder water (and decided that softening it at the municipal level wouldn’t be cost-effective). If there was fine grained data available about water hardness and obesity levels, that might provide at least a little signal.