How Much Water Can Concrete Hold?

Get an easy rule of thumb for determing whether concrete will crack under the weight of contained water – in this case, an aquaponic garden.

LESLIE: Patrick in Tennessee is on the line and needs some help with a water feature. What can we do for you?

PATRICK: I have an aquaponic garden that was in the yard at our old house. When we moved, this new house is pretty much all pool and concrete in the back. And this aquaponic garden, it’s basically about 150 gallons of water and 150 pounds of lumber that occupies about a 5×2½-square-foot area. And I’m just concerned if I put it on the concrete, if it’ll crack.

TOM: So you’re worried about the concrete cracking underneath it?

PATRICK: Correct.

TOM: And what are you talking about? Like a concrete driveway? A concrete sidewalk? What are we talking about?

PATRICK: It’s like a slab that goes around the pool.

TOM: What’s the tank size? It’s 200 gallons, did you say?

PATRICK: There’s two tanks, one mounted above the other. So one’s 100 gallons and one’s 50 gallons.

TOM: So 150 gallons times 8 pounds per gallon, so you have over 1,000 pounds of water there, plus the lumber. That’s not terrible. I mean think of it: that’s like four or five people standing on the concrete together.

PATRICK: OK.

TOM: So I think it’d probably be OK. You know, it really depends on how thick the concrete is and that sort of thing. But generally speaking, concrete should be able to take folks standing shoulder to shoulder all around it without a problem.

PATRICK: Well, thank you so much.