Standing on a groundsheet increases the pressure on any water underneath.
From the en.wikipedia.org
Up to 6 adults can stay in each tipi and each one comes with a groundsheet and raincatcher.
From the en.wikipedia.org
A groundsheet is used to provide a waterproof barrier between the ground and a sleeping bag.
From the en.wikipedia.org
With single skin tents, the groundsheet may be sewn in or separate.
From the en.wikipedia.org
An optional tent footprint or groundsheet protector may be used.
From the en.wikipedia.org
French camping is not at all the same as British camping, and this suits me down to the groundsheet.
From the telegraph.co.uk
You can stand up in it and a 300cm x 100cm waterproof groundsheet is sewn into the inside of the tent.
From the couriermail.com.au
If you can afford it, snap one up, and if you're feeling flash, a carpet and footprint groundsheet is available too.
From the independent.co.uk
None of the soldiers was wearing a combat jacket or head net and a groundsheet had been flapping in the breeze.
From the en.wikipedia.org
More examples
A waterproofed piece of cloth spread on the ground (as under a tent) to protect from moisture
A tent is a shelter consisting of sheets of fabric or other material draped over or attached to a frame of poles or attached to a supporting rope. While smaller tents may be free-standing or attached to the ground, large tents are usually anchored using guy ropes tied to stakes or tent pegs. ...
A sheet of waterproof material that is spread on the ground, often beneath a tent, upon which a person may sit or sleep
A lining for the base of a tent or awning which shields the occupants from the ground. See also awning carpet.