Future Solution
New Technology
One of the possibilities that would prevent running out of resources is to implement vertical farming. This new technology would allow for increased food production to sustain higher populations. It increases food production because it is a vertical building that will have numerous floors each floor growing a different crop. This design will also limit the amount of land needed to grow a lot of food this will be important because with the increase in population there will be more buildings and land will be more scarce also buildings and farms will need to take up less space.
http://www.ecofriend.com/entry/vertical-farming-the-new-agriculture-option-for-the-future/
http://www.ecofriend.com/entry/vertical-farming-the-new-agriculture-option-for-the-future/
Mining
The other solution to dwindling resources is to mine other planets for the metals. However if we wanted to get more water we'd have to find a planet that has it. This will cost trillions of dollars and will not be very cost efficient unless new technology is discovered or Earth is in desperate need of the resources. This solution would also be highly controversial because humans would be exploiting planets and breaking the treaty used for creating the international space station: essentially don't disrupt or damage celestial bodies.
http://news.discovery.com/space/mars-prospecting-ores-gold.html
http://news.discovery.com/space/mars-prospecting-ores-gold.html