How can I avoid ordering multiple bottles of water at a restaurant?

In France it is required by law to provide tap water to a customer, for free. It is very common and acceptable to ask for tap water in a pitcher in a restaurant. Don't hesitate to ask for a refill.

In my experience, places where waiters may frown upon customers ordering tap water will happily accommodate you if you order a paid drink with it. Just order yourself an aperitif or a glass of cola / juice / beer, and ask the waiter to bring a pitcher along. This way, the restaurant still makes the profit they expect to make, and you get enough water.

I am French myself, and i traveled a lot in my country.

I've never found a place where they wouldn't (or would reluctantly) serve tap water. Maybe in very expensive restaurants (i doubt it, but why not), but anywhere else it's totally okay.

I may want to add the specific case for Austria: You can order tap water ("Leitungswasser") in almost any restaurant here. They will charge you a small amount (mostly for the service of bringing the water to your table, washing the glass after use).

Be aware that "Stilles Wasser" (Still water) will be bottled and expensive as it is mineral water. A useful hint by martin.koerbel from the comments: If they charge for "Leitungswasser" they will need to reflect that fact in the menu, so you can look up the price for it before you order it. If it is not listed there it will - most certainly - be free (although I did encounter places where this was not the case).

Source: I live in Austria and have been to most of the parts in the country. As I am without a regular income tapwater is the way to go in restaurants.

I'm in Europe, and have travelled in many European countries over many years.

I can count on the fingers of a hand, the times I haven't been able to say "a glass of tap water please". That includes pubs that make most of their money from drinks. Perhaps "once in 4-5 years" kind of frequency, that rarely.

If needed, "sorry, but I have a medical condition and need tap not bottled water, can I have a jug of tap water, thank you".

If they say no, say "okay then, thank you" courteously, and leave. Change where you are for anywhere else.

You got a healthy amount of answers and comments, but I see no concise part about Germany, so let me add that:

While in France you get your unlimited supply of tap water by law, in Germany - at least in all places I visited so far, mostly in the south - waiters do understand the word "tap water" (well, Leitungswasser). They do not get offended, but they will not actually go to a tap and let out our excellent and healthy tap water, but they will very likely open a bottle of still water.

In other words, hereabouts, the word "Leitungswasser" is a synonym for "Stilles Wasser" (still bottled water), at least it is understood as such by waiters. They generally, in my experience, won't raise a brow, but you will pay whatever you have to pay for still water.

When going out with many people, it is common to order bottles of water for the table; indeed I have never seen pitchers of clear water. You can get some alcoholic beverages in pitchers, but in my experience not still water.

Everything said so far aside: most waiters around here are human though, and you might just try to order "one glass of XXX, and I need to drink a lot for my stomach, could you please also bring a large jug of simple Leitungswasser". 99% they will happily respond "sure! I'll bring you a large bottle" (and you will pay for it), but you might just meet the 1% who indeed is able to fetch some vase and fill it to the brim with actual tap water from a tap.

But I would not suggest leaving the restaurant if they can only bring bottles - you might find yourself starving (and thirsty!) after a few days...

There's nothing weird in ordering a few bottles of water, however it would be more economic to order one big bottle instead of few smaller ones (if the restaurant has it in menu).

However, if you expect to get 4 bottles in the price of 1 because you need more water, it's similar like asking a double steak in a price of 1, because your body needs more proteins.

Restaurants are generally expensive and for some people they are more expensive than for others.

Drinks are the main income source for restaurants in Germany, so it's not very likely you find one that will offer drinks for bulk price. If so, they'll have to get their money in some other way. Either the quality would be lower, or the food will be more expensive.

Other answers have touched upon some of these, but to recap here are some strategies you can use:

• Don't feel shy and order tap water as often as you need. It's extremely common and totally unproblematic in France. Most waiters/restaurateurs expect it and won't think twice about it, only the most upscale restaurants expect you to buy bottled water. It's not so common in Germany but still worth a try. The only “regular” place (i.e. beside remote islands or mountain hut where water supply is scarce) I have seen a waiter flat out refuse to serve tap water was Luxembourg.
• Order large (1L) bottles. I can't tell if you meant 4L or 4 individual 33cl bottles but if you meant the latter then switching to large bottles would make it easier. Just ask for a “large” bottle of (flat) water. In Germany, water tends to be carbonated if you do not ask specifically. While not completely idiomatic asking for water “without gas” may be the safest way to make yourself understood if you are not comfortable speaking German.
• If you still have some qualms about ordering water, order a drink at the beginning of the meal, maybe some soda, juice, or a beer to drink before your food. That way you don't come across as cheap and the restaurant gets to make a profit on the drinks so you can feel free to ask for tap water. Same thing if your party is having a bottle of wine or something, asking for water next to it is completely normal.

The only times in Europe I've not been able to get more than a glass of water (though I've never asked for several liters for me alone) in a restaurant was in parts of Spain during a severe drought, when water rationing was in effect.

And even in those cases they're usually more than happy to sell you any amount of bottled water (carbonated and still both) as long as they have it in stock.

One trick that can help in Germany if you're somewhere that doesn't have large bottles of water is that alcohol-free hefeweizen is widely available, sometimes cheaper than water, and the standard size is a half liter.