When they first arrive in Spain, many people are unsure if the tap water is safe to drink or not, but according to the Spanish Ministry of Health, at least 99.5 percent of Spain’s water supply is safe to drink.

Spain’s Organisation of Consumers and Users (OCU) also confirms that tap water in Spain is generally good quality and is a good alternative to bottled water. Of course, it’s cheaper than bottled water too.

READ ALSO: Why does tap water taste strange in some parts of Spain?

Despite this claim, there are several areas in Spain that don’t have good-tasting tap water, leading to the necessity for filters or even buying bottled water instead.

The OCU, who carried out a comparative analysis of the taste of the tap water around Spain, has revealed that the taste of the water is directly related to how hard or soft the water is. In other words, the harder the water, the worst it tastes.

The hardness of the water is caused by the amount of minerals in the water like lime and magnesium salts. “In areas of Spain where the water is hard, it tends to have a bad taste. In these areas it is common to use natural mineral water as table water,” the OCU said.  

How hard or soft your tap water is can also affect the way your clothes are washed or even your hair. If you live somewhere with soft water, you’ll see more bubbles created from the detergent you put in your washing machine. Your clothes will also stay bright for longer and form fewer bobbles. If you live somewhere with hard water, the opposite can be true. You’ll also need more shampoo for it to create a lather on your hair.  

The OCU study found that the softest, and therefore the best tasting tap water, can be found in the areas of Galicia and in Castilla y León, specifically the cities of Burgos, León and Valladolid, as well as in Madrid.

Both Extremadura, the Basque Country and the Canary Islands also have soft tap water. And in the Valencia region, it’s Alicante where the softest water is found.

On the other end of the scale, the hardest water and the worst tasting can be found in Almería in Andalusia, Valencia city and in the Aragonese provinces of Zaragoza and Teruel.

Only slightly better, but still pretty hard and with a disagreeable taste are the provinces of Murcia, Albacete, Jaén, the Balearic Islands and Tarragona, areas across Murcia, Castilla-La Mancha and Catalonia.  

And finally, the areas with only slightly hard water are Asturias, Navarre and La Rioja; Barcelona and Girona in Catalonia; Cádiz, Seville and Granada in Andalusia; and Ciudad Real in Castilla-La Mancha.

Of course, the taste of the tap water is not down to the hardness or softness alone. It could be due to the number of chemicals added such as chlorine, the type of filtration process and where the water comes from in the first place, whether rivers or reservoirs and the type of water they have too.