This sentence mainly examines the sentence pattern of There be, which is a commonly used sentence pattern to express "existence"

In the sentence, there are several water bottles on the ground, but they are very small:

Being means "having";

Several means a little, a few, etc.

Water bottles refer to water bottles, water bags, kettles and so on.

In this sentence, On the ground means "on the ground" and small means "very small, very small".

There are some water bottles on the ground, but they are small.