Jaytee wrote:
How thick should a concrete slab tank base be to support a water tank holding 5000 gallons of water?

Answer:
Jaytee,
Thanks for the question. The answer depends on the size of the tank's "footprint" and the method of support. Let's assume the weight of the water and tank is around 44,000 lbs. If it is a rectangular tank... say 10'x10'x6' tall, an 8" slab (properly reinforced) would be fine. If it is standing up on end... say 8' diameter and 13' tall and resting on 4 legs, you have an 11,000 lb load at each point. You could then use a thinner slab and just thicken the concrete to around 12" (properly reinforced) at each bearing point. Hope that helps. If you want to convey additional information, I could more specifically answer your question!