How Much Water Do Trees Save?

This young oak tree will collect 654 gallons of stormwater runoff this year. How much will it collect in 20 years?

by Bonnie Allen

When I moved here 45 years ago, there was a coast live oak sapling in my backyard. Now it’s a mighty tree, shading 30 feet of yard behind my house. I’ve learned that this oak is not just beautiful; it’s a water saver as well. How much water? Well, 2,847 gallons, according to a new online tree benefits calculator. I entered my location, the type of tree and the trunk diameter. You can see the results for my tree here.

Trees save water by keeping it on the property instead of allowing it to run off in storm drains. They do this in several ways. By collecting water on their leaves, they slow the rate of runoff to the ground, also reducing soil erosion from runoff. The shade they provide slows evaporation from the soil. And they store water in their root systems. 

I’ve had occasion to do some digging under my oak tree--not recommended, since oaks don’t like the ground disturbed under their canopy. I was astonished to discover that even in August in a severe drought year, there was still moisture 4 inches down. 

It looks like drought is becoming a long-term problem in our neck of the woods. Planting more trees is one way to combat drought. (Plant trees when the rainy season begins, so they can get a head start when they don’t need to be watered.)

If you checked the link to my tree benefits, you saw that the app also calculates benefits to property values, energy savings from cooling, improved air quality, and removing climate-damaging CO2 from the atmosphere. It pegged the dollar value of my tree at $164 a year--not a lot, but nothing to sneeze at. Multiplied by the four mature oak trees (and one teenager) on my property, it adds up. 

Just how valuable are the trees on your property? Use the National Tree Benefit Calculator to find out.