Why is water said to have a V shape?

Water has a v shape because the hydrogen atoms form an angle with each other.

While many 3 atom molecules form a bar, such as carbon dioxide, hydrogen monoxide is bent. The reason has to do with valence electrons and the bond types between the atoms.

Carbon dioxide will be our example of a bar shape. Carbon has 4 valence electrons, or 4 electrons in it's outer shell. Oxygen has 6 electrons in it's valence shell. All atoms but hydrogen and helium are going to want a full octet in the valence shell, or 8 electrons (except hydrogen and helium, as they have an outer shell of 2 possible electrons). Luckily, they can share electrons in what is called a covalent (co-valent, or in the same valence) bond. In this case, the carbon will form a double bond with both oxygen atoms, meaning it is sharing 2 electrons with one oxygen and 2 with the other. Because of this, there are no weird forces on the molecule, and the atoms form a bar.

In water, or dihydrogen monoxide, you have 2 hydrogen atoms and 1 oxygen atom. The oxygen has 6 valence electrons and each hydrogen has one. Together, they have 8 valence electrons. The hydrogen will form single bonds with the oxygen, and as the oxygen gets it's two, they each get one. 

However, there are still 4 electrons that are not in bonds. These two electrons on the oxygen form what are called lone pairs; the four electrons will split up into groups of two. In an attempt to get away from each other, as negative charges tend to do (think the similar ends of magnets repelling each other), the lone pairs and hydrogen atoms will form a tetrahedron  around the oxygen atom. 

Because we only show the hydrogen atoms and not the lone pairs around atoms, the models of hydrogen monoxide are all bent.