Can you drink the tap water in San Pedro de Atacama?
Quick answer
No. Drink bottled or treated water. The reason is not poor sanitation but natural geology: the rivers that supply this part of the Antofagasta Region carry arsenic dissolved out of volcanic rock, and published research puts regional concentrations well above the World Health Organization guideline.
This is unusual advice to have to give in a middle-income country with generally good water infrastructure, and it is worth being precise about. The problem is geological rather than a failure of treatment. Peer-reviewed work on the Antofagasta Region documents arsenic in the Río Loa and its tributaries at concentrations far above the WHO guideline of 10 micrograms per litre, and describes populations of the Atacama having been exposed to naturally occurring arsenic for thousands of years.
Where it comes from
The rivers that feed this region rise in volcanic terrain, and arsenic leaches out of that rock into the water. Published studies of the Antofagasta Region report arsenic in the Río Loa system at levels ranging into the milligrams per litre in some springs — orders of magnitude above the WHO drinking-water guideline of 10 micrograms per litre. It has been there far longer than the town has.
What is done about it
Chile has invested substantially in arsenic removal for the region's drinking water over several decades, and treatment plants with reverse-osmosis modules serve settlements in the area. We are not able to verify the current arsenic level in San Pedro's specific supply from a public source, which is precisely why this page does not quote a figure for the tap you will be standing at.
What to actually do
Drink bottled or filtered water. Every shop in San Pedro sells it and every hotel provides it. This is what residents and visitors alike do, and nobody will think the question odd.
The plastic problem
You will get through a lot of water here, because at 13 to 38 per cent humidity you lose it constantly. A bottle with a filter that handles dissolved contaminants — not a basic carbon filter, which does not remove arsenic — is the alternative to buying several litres of plastic a day. Check the specification before you rely on it.
How much you need
More than you expect. A litre for a half-day excursion and two for a full one is the working figure, and at 4,000 m you should be drinking steadily rather than when thirsty. Dehydration and altitude sickness produce overlapping symptoms, which makes it easy to blame the wrong one.
What about ice, and brushing your teeth
Restaurants serving visitors use treated water for ice. Brushing your teeth with tap water is not the concern here — arsenic is a long-term exposure issue rather than an acute one, and a week of incidental contact is not what the research is about. The advice to drink bottled water is about the water you actually drink.
Frequently asked questions
Why can't you drink the tap water?
Natural arsenic from volcanic rock in the rivers that supply the region, documented in peer-reviewed studies of the Antofagasta Region. It is geology rather than poor treatment.
Is it dangerous for a short visit?
Arsenic exposure is a long-term health issue rather than an acute one. The sensible course for a week's visit is simply to drink bottled or filtered water, as everyone there does.
Will a travel filter work?
Only one specified to remove dissolved arsenic. A basic carbon filter will not. Check the specification rather than assuming.