# Grooves on water tank

Why are there grooves on almost every water tank? Just typing water tank in Google images would reveal what I am talking about. And here is a sample picture!

I think it would mostly be regarding water pressure. Please share your knowledge.

• maybe for tying some elastic band to the tanks, like when you want to hold them together or you want to place some pipe on the side of the tank. Just guessing.. – AoZora May 15 at 7:42
• Something interesting you might notice (and it relates to the answer) is that typically you see this done for non-carbonated beverages, but for carbonated drinks they often don't bother. – JMac May 15 at 11:05

$$\sigma_=\frac {My}I$$
But why don't they just bulge the whole think out? (That should provide even more resistance to bending). The answer is that though it does increase the resistance to bending, it also increases the shear stress between adjacent layers. The right balance is obtained by implementing an $$I$$-beam shape. They make multiple $$I$$ beam shapes in the form of grooves.