Where does the water go once it exits the downspout?

Your roof has a tremendous surface area that is excellent at collecting water during a rain storm. Hopefully all that water is going to a gutter and eventually to a downspout. Where does the water go once it leaves the downspout? Ideally, the downspout is connected to a perimeter or stormwater drain so that water is taken away from your foundation. Frequently, water is pooling at the downspout and can make its way to your foundation and lead to a very wet crawlspace or structural damage. 

Downspout without a splash block or connection to a drainage system. All the water is pooling next to the foundation and can lead to issues with a wet crawlspace.

Water from this downspout goes directly to the foundation. Not ideal and a good way to cause long term damage.

Take a look at the downspouts at your house. Are they connected to a drain system or are they able to spew water on the ground next to your house? If the downspout ends at the ground like the above pictures, you have a potential problem. All that water can erode the dirt around the foundation and lead to moisture penetration at the foundation and in to the crawlspace. An easy fix is either a splash block or a downspout extension (pictures below). They need to go at the end of the downspout and placed so that they direct water away from the house. 

This is the ideal solution. A downspout connected directly to a perimeter drain system that leads to a stormwater drain.

The green splash block is the right idea but poorly executed in this picture. This splash block needs to be turned 90 degrees so that the water is directed away from the house and towards the grassy area.

Down spout extension. Again, this is the right idea but it needs to be connected to a downspout to work.