Which is the reason that there is so much difference in the price of bottled mineral water between European countries? For example in Greece a 0,5 lt bottle costs 0.5 euro but in e.g Italy, Germany or UK the same quantity is about five times higher. After all water is very important and crucial and in the majority of the countries access to public tap water is limited.
I am not aware of such difference in price for bottled water. I haven't been in Greece yet, but in most European countries I bought bottles of water for less then 50 ct per liter. That is in local supermarkets.
Could it be that you are comparing prices in bars and restaurants? Usually tap water is of high quality. In France for example, you can order still water or sparkling water in which case you pay between 2 and 4 euro. You could also ask for a carafe of water which usually is free of charge.
In most cases people just pay for the brand or because they consider it more appropriate for their social class.
So if there is a price difference it boils down to demand and availability. If most people drink tap water, only the upperclass drinks bottled water, who can afford high prices. Also with less people drinking bottled water, less quantities are needed, increasing the cost for transportation
The answer is: The price is actually not that different. I travelled most of the European countries and mostly lived from food and drinks bought in local supermarkets. If you know where to buy, water isn't expensive in any european country. For example, in Germany you get a 0,5 l bottle of water for less than 15 cents (plus deposit of 25 cents). Actually, you won't find cheaper water in Spain, Italy, France, Great Britain, Sweden, Belgium etc. - but maybe in eastern europe. However, even in very expensive countries like Switzerland, Norway or Iceland you won't have to pay more than 50 cents per litre. But note that the latter three countries don't have Euro, but their own currency and a more decoupled economy which explains the difference.
So why do you think, the price is so different?