For a start you can get bigger cages. I use a Topeak Modula EX sometimes, which is adjustable to ⌀74 mm (also for the Modula II, with a metal clip instead of plastic). This is noticeably bigger than a standard cage, and is good for many sizes bottled water is sold in. The Modula range might include the biggest bottle holders: the Modula Java is meant for insulated mugs, has an extra strap for the top, and extends in height as well as width.

Then there are luggage cages (e.g. Salsa Anything Cage, Topeak Versacage, both rated to 3 kg) that would also work for big bottles (like 2 l mineral water bottles), while being designed more for things like tents. You might want an extra strap though (these cages come with straps), as the length and weight of a big bottle make it less secure. Loaded they might not fit under your toptube, and might be too wide for pedalling.

The biggest normal diameter bottle I've got is the 1 litre Zefal Magnum, but there's at least 1 other 1 l bottle on the market (SiS). They don't fit all frames for height. I did recently ride with two Magnums, plus another 800 ml in my saddlebag. That was about half what I needed, but I didn't fancy 200km with a backpack, so planned my refill (this was after the worst of our lockdown, but before everywhere re-opened). I know people who regularly go that far with several kilos on their backs.

I have a suspicion that there's a historical reason - standard cages are the perfect size for a bottle of wine, and both France and Italy contributed a lot to bicycle standards.

The picture below illustrates a few of my points (in this answer and in comments):

• There are cages on the forks. I can't see from my picture how I mounted them and it was a few years ago, but although cable ties were definitely involved, they weren't the only fixing, and even without the mudguard it would have taken a hard crash to push the bottles into the wheel. That's something you have to be careful of.
• The fork cages are Topeak Modula EX (actually one is a fake)
• Note the wine bottle in the seat tube cage (and stove fuel under the down tube)

This was loaded more for bike camping than touring, with 35 kg of luggage. The front panniers held walking boots and a wetsuit, and I only did 2×30 km like this - but rather hilly.

For a start you can get bigger cages. I use a Topeak Modula EX sometimes, which is adjustable to ⌀74 mm (also for the Modula II, with a metal clip instead of plastic). This is noticeably bigger than a standard cage, and is good for many sizes bottled water is sold in. The Modula range might include the biggest bottle holders: the Modula Java is meant for insulated mugs, has an extra strap for the top, and extends in height as well as width.

Then there are luggage cages (e.g. Salsa Anything Cage, Topeak Versacage, both rated to 3 kg) that would also work for big bottles (like 2 l mineral water bottles), while being designed more for things like tents. You might want an extra strap though (these cages come with straps), as the length and weight of a big bottle make it less secure. Loaded they might not fit under your toptube, and might be too wide for pedalling.

The biggest normal diameter bottle I've got is the 1 litre Zefal Magnum, but there's at least 1 other 1 l bottle on the market (SiS). They don't fit all frames for height. I did recently ride with two Magnums, plus another 800 ml in my saddlebag. That was about half what I needed, but I didn't fancy 200km with a backpack, so planned my refill (this was after the worst of our lockdown, but before everywhere re-opened). I know people who regularly go that far with several kilos on their backs.

I have a suspicion that there's a historical reason - standard cages are the perfect size for a bottle of wine, and both France and Italy contributed a lot to bicycle standards.

The picture below illustrates a few of my points (in this answer and in comments):

• There are cages on the forks. I can't see from my picture how I mounted them and it was a few years ago, but although cable ties were definitely involved, they weren't the only fixing, and even without the mudguard it would have taken a hard crash to push the bottles into the wheel. That's something you have to be careful of.
• The fork cages are Topeak Modula EX (actually one is a fake)
• Note the wine bottle in the seat tube cage (and stove fuel under the down tube)
• A total of 5 cages.

This was loaded more for bike camping than touring, with 35 kg of luggage. The front panniers held walking boots and a wetsuit, and I only did 2×30 km like this - but rather hilly.

For a start you can get bigger cages. I use a Topeak Modula EX sometimes, which is adjustable. This range might include the biggest bottle holders, but there are luggage cages that would also work for big bottles, while being designed more for things like tents. You might want an extra strap though, as the length and weight of a big bottle make it less secure.

The biggest normal diameter bottle I've got is the 1 litre Zefal Magnum, but there's at least 1 other 1 l bottle on the market. They don't fit all frames for height. I did recently ride with two of those, plus another 800 ml in my saddlebag. That was about half what I needed, but I didn't fancy 200km with a backpack, so planned my refill. I know people who regularly go that far with several kilos on their backs.

I have a suspicion that there's a historical reason - standard cages are the perfect size for a bottle of wine, and both France and Italy contributed a lot to bicycle standards.

For a start you can get bigger cages. I use a Topeak Modula EX sometimes, which is adjustable to ⌀74 mm (also for the Modula II, with a metal clip instead of plastic). This is noticeably bigger than a standard cage, and is good for many sizes bottled water is sold in. The Modula range might include the biggest bottle holders: the Modula Java is meant for insulated mugs, has an extra strap for the top, and extends in height as well as width.

Then there are luggage cages (e.g. Salsa Anything Cage, Topeak Versacage, both rated to 3 kg) that would also work for big bottles (like 2 l mineral water bottles), while being designed more for things like tents. You might want an extra strap though (these cages come with straps), as the length and weight of a big bottle make it less secure. Loaded they might not fit under your toptube, and might be too wide for pedalling.

The biggest normal diameter bottle I've got is the 1 litre Zefal Magnum, but there's at least 1 other 1 l bottle on the market (SiS). They don't fit all frames for height. I did recently ride with two Magnums, plus another 800 ml in my saddlebag. That was about half what I needed, but I didn't fancy 200km with a backpack, so planned my refill (this was after the worst of our lockdown, but before everywhere re-opened). I know people who regularly go that far with several kilos on their backs.

I have a suspicion that there's a historical reason - standard cages are the perfect size for a bottle of wine, and both France and Italy contributed a lot to bicycle standards.

The picture below illustrates a few of my points (in this answer and in comments):

• There are cages on the forks. I can't see from my picture how I mounted them and it was a few years ago, but although cable ties were definitely involved, they weren't the only fixing, and even without the mudguard it would have taken a hard crash to push the bottles into the wheel. That's something you have to be careful of.
• The fork cages are Topeak Modula EX (actually one is a fake)
• Note the wine bottle in the seat tube cage (and stove fuel under the down tube)

This was loaded more for bike camping than touring, with 35 kg of luggage. The front panniers held walking boots and a wetsuit, and I only did 2×30 km like this - but rather hilly.