Rail bosses have raised the prospect of buying up more land in the Waterloo area to increase the capacity of the station.
Network Rail's strategic business plan for the five years from 2014 – published earlier this month – includes a section discussing options for future growth beyond 2019.
The document mentions "consideration of land take in the Waterloo area to improve the approaches into the station" as one of the possibilities that Network Rail will need to examine if it is to meet the projected demand for train services by 2031.
The railway viaduct in the Waterloo area was last expanded in the early 1990s when the now-disused Waterloo International Terminal was built.
Tim Shoveller, managing director of the Network Rail and South West Trains joint venture which runs trains and track into Waterloo, said: "The route out of London Waterloo across the south and south west of England is one of the busiest in Europe, with Waterloo Station alone handling around 100 million passengers per year – a figure which will only rise in the years to come.
"More passengers create a need for more trains which places an even greater demand on an aging infrastructure which is 175 years old in parts. We will be investing heavily in increasing the network's resilience and reliability and doing everything we can to be able to provide a railway which can accommodate the extra trains needed to cope with growing demand.
"Despite the large investment which will deliver huge benefits to passengers through to 2019, there will have to be trade-offs to deliver them. As passenger and train numbers rise, the number of challenges increase and it becomes more complex than ever to run a reliable and cost-effective railway.
"As a result, we have entered an era of trade-offs and will increasingly have to balance the need to build and renew more infrastructure, run trains on time and reduce costs."
The Government last year announced funding for a £350 million project to expand capacity at Waterloo but details of the proposals are scarce.