How many gallons does a standard water can hold?

A standard watering can typically holds about 2.0 gallons of water. This size is commonly used for both household gardening and more extensive landscaping tasks, as it strikes a balance between being manageable and providing enough water for various plants. The choice of 2.0 gallons reflects the typical capacity that accommodates everyday use without being too cumbersome.

While it is true that some watering cans may come in differing sizes, the most common standard found in many households and gardening centers tends to be around this capacity, making it a practical choice for most users.

In terms of the other options, while 1.5 gallons, 2.5 gallons, and 3.0 gallons are capacities that exist in various watering can designs, they are not as universally recognized as the 2.0-gallon standard for everyday use. Thus, this choice is well-suited for the context of the question.