Our astronauts will be settling on Mars indefinitely. It's not feasible to send water, oxygen and food from Earth to the astronauts: they will produce those on Mars.
On Mars, water can be extracted from the soil. The rover will select the location for the settlement primarily based on the water content in the soil. We expect this to be at a latitude of between 40 and 45 degrees North latitude. Water extraction will be performed by the life support units. The rover will deposit soil into a water extractor in the life support units. The water extractor will heat the soil until the water evaporates. The evaporated water will be condensed and stored, the dry soil expelled, and the process repeated to extract more water.
About 1500 liters of reserve water will be stored in each life support unit, which will be consumed primarily at night, and during periods of protracted low power availability, for example during dust storms.
Since Mars has gravity, water can be used in the same way as on Earth. Each astronaut will be able to use about 50 liters of water per day. The water will be recycled, which takes much less energy than extracting it from the Martian soil. Only water that can not be recycled will be replaced by water extracted from the soil.
Oxygen can be produced by splitting water into its constituent parts, hydrogen and oxygen. The oxygen will be used to provide a breathable atmosphere in the living units, and a portion will be stored in reserve for conditions when there is less power available, for example at night, and during dust storms.
The second major component of the living units' atmosphere, nitrogen, will be extracted directly from the Martian atmosphere by the life support unit.
When the astronauts land on Mars, there will be storable food from Earth waiting for them to use. The storable food from Earth will only serve as emergency rations, which means the astronauts will try to eat as much fresh food that they produce on Mars as possible. It is likely that algae and insects will also be part of the diet on Mars.
Food production will occur indoor under artificial lighting. In total, there will be approximately 80 m2 available for plant growth in the original habitat. The first crew will also be able to use the habitat of the second crew to grow food because the hardware for the second crew lands only a few weeks after the first crew lands.
A thick layer of Martian soil on top of the inflatable habitat will protect the plants (and the astronauts) from radiation. CO2 for the plants is available from the Mars atmosphere and water is available through recycling and the soil on Mars. Nutrients for the plants could come from recycling human waste or could be imported from Earth.
Any plant production surplus will be stored as emergency rations for the second crew and for emergencies. Non-edible parts of the plants will be recycled or stored until more advanced recycling equipment is shipped from Earth.
Mars One will investigate the volume requirements for food production in the simulation outpost and the crews will be trained for many years to operate the greenhouse equipment. The aim is for colony to be independent from the food they receive from Earth. There will always be enough emergency rations in storage, locally produced or from Earth, to survive until the next supply mission comes.