The solution is to tell them why clean water matters, and provide them a cheap way of making dirty water pretty clean. Ie. a water filter.
The cheapest water filters, costing perhaps $10 and able to filter a family drinking water supply for years, will still eliminate most concerning contamination in water.
The best water filters - pumped reverse osmosis systems - are still only a few hundred dollars, and will also give a family drinking water for many years.
In thailand for example, vending machines exist which cost a few cents to use and will dispense a few liters of filtered water. These help spread the cost of the expensive filter between people and across time.