Generally, water along the
Camino Frances is safe to consume. However, and especially during the hot and dry summer months, local wells are stressed. Many of the wells that supply agricultural water as well as the trail-side fountains, especially in heavily agricultural areas, were not drilled very deep. Over the years many wells have become contaminated with various fertilizers and other compounds sprayed on the crops and fields.
Some fountains have "not potable" signs. On others you take your chances. As a general rule though, people are not dropping like flies.
However, on the stretch of Meseta from Carrion de los Condes to about Sahagun there have been reported GI illnesses, presumably from drinking from the old fountains that abound along the Camino. So, pilgrims are advised to depart Carrion de los Condes with enough bottled water to make it the next 30 - 40 Km to Sahagun as there are few places with known safe water all year long.
In May 2014, I departed Carrion with 5.5 liters of water. By the time I reached a friend's home in Moratinos 31 Km and over 7 hours later, I was down to half a liter. But, I had been sharing my water with other pilgrims who needed it along the way.
As a general statement, if the water comes from the tap in an albergue, hostal, hotel or cafe/restaurant, it can be presumed to be safe. I am leary of "out in the open" or ancient fountains if I do not know the water source. Many of these free-flowing fountains appear to be springs that run just below fields with grazing farm animals. How do you take your "cowpie?"
Everyone has a tolerance level for naturally occurring spring water. If you are not prone to GI illness or do not have an impaired immune system, I would say go for it. However, if you are like me and either get "jelly belly" easily, or have any medical condition where you must be more careful regarding water sources, DO buy bottled water. It is cheap and readily available. On the other hand, I also carry a generous supply of an antidiarrheal medication, just in case.
PLEASE SAVE THE EMPTY PLASTIC BOTTLES FOR REUSE, OR RECYCLE THEM APPROPRIATELY. Please, do not litter along the Camino.
I hope this helps.