The United States has the most advantageous both geographic and material environment with concerns to water.
Coastlines and Oceans
The United States has exposure to the two most important oceans, an advantage shared by only notably Canada and Mexico. Both of its coastlines are long and pocketed with multiple naturally advantageous places for ports. It has the longest practical coastline. Its ships can easily travel to Europe, Latin America, West Africa, Oceania, and East Asia. It also has little difficulty traveling to the third important ocean, the Indian, given its exposure from the east and west. This gives it a tremendous place to dominate the seas both in terms of trade and military.
Canada has exposure to both big oceans, but it is so barren and non-densely populated that it has little chance of becoming an oceanic power. Mexico also is exposed to both oceans, but its population is primarily on the interior only connected to the sea by a scattered river system. It certainly is and will grow as an oceanic power, but it is destined to always be secondary to its neighbor to the north.
India has a great long coastline, but its position in the Indian Ocean means it will at most be a regional power, it doesn’t have the incentive nor reach to dominate either of the larger oceans. China has a long coastline with lots of natural places for ports, but it is constrained by island chains. To enter the Pacific, its ships have to pass through territorial waters of Russia or Japan. To enter the Indian and Atlantic oceans, it has to pass through the contentious South China Sea, where the Philippines, Malaysia, and Vietnam among a few others have claims. Even without this issue in this sea, it has to travel through the tight Strait of Malacca or various Indonesia straits, giving these countries leverage over it.
The United States has none of these issues, it has two long coastlines which are great for ports on both key oceans. It has by far the world's most advantageous coastline.
Navigable Rivers
America also has the best system of navigable rivers. Its Mississippi/Missouri is an easily navigable river basin which covers a huge swath of highly productive flat land great for both agriculture and cities. Various other rivers in the United States such as the Colorado, Connecticut, Susquehanna, Chattahoochee, Rio Grande, Brazos, Hudson, Columbia/Snake, and Sacramento/San Joaquin also have productive basins (to varying degrees) and are navigable. The Mississippi is the foundation of agriculture in the United States. Without it, American food would be expensive to transport and not globally competitive, but with it, the US has the capacity to cheaply produce enough food to be self-sufficient (though it chooses not be).
The Mississippi River basin is the fourth largest river basin in the world, behind the Amazon, Congo, and Nile. The Nile has cataracts which impede navigability, and includes relatively unproductive land. The Congo basin is made primarily of inhospitable jungle and has notable sections of rapids. The Amazon does not share the rough sections of the other two rivers, but its water comes from the enormous impenetrable Amazon rainforest, so its strategic value is greatly limited.
Corn from Iowa can be cheaply shipped by barge through New Orleans out for processing. China has some rivalry with its rivers, but its land isn’t as productive and its rivers aren’t as unified. Northern Europe also has highly navigable rivers and very productive land, but it doesn’t encompass a very large area. The United States has absolutely the best river system.
Water Sources
The United States also doesn't rely on any other country for its water. Egypt for example, is highly dependent on downstream nations for the Nile, which is the lifeblood of its entire country. This is a huge piece of leverage that makes Egypt vulnerable. This is true too with Vietnam, India, Bangladesh, Uzbekistan, Nigeria, Mozambique, Uruguay, and most of Europe with their respective up-river nations. The water which flows in US rivers originates from within its borders. It has no issues with the source of its water.
Supply and Scarcity
Many countries, often connected to the previous issue on the source of their water, have issues with supply. China for example, north of the Yangtze has major issues with its water supply due to lack of rain. Countries in Africa and on the Indian subcontinent have supply-related issues similarly due to lack of rain, and inefficient agricultural hydration methods make the issue worse. Though there are some concerns with water scarcity in California, in the east and northwest, rainfall is more common than anywhere in the world outside a rainforest.
Clean Water
Though this is not spesifcally a geographic advantage, the US’s water resources are fairly clean. The Yangtze, Niger, Congo, Ganges, and Indus rivers are all highly polluted. US rivers are not as safe as tap water, but they don’t have dangerous levels of pollution. The Great Lakes, which hold an enormous amount of freshwater, are very clean, having significantly improved in the last fifty years. Water for human consumption is prevalent and generally a non-issue in America.
Conclusion
The United States has the best relationship with water of any country with its doubly exposed coastlines, huge basin of navigable rivers, water being sourced within its borders, and safe water quality.
(This isn’t greatly written by any means, it’s just meant to convey a general concept about one aspect of America’s geographic strength.)