sentences:  Speaking at TED in 2009, Pritchard estimated that by using the LifeSaver bottle, reaching the Millennium Development Goals of halving the number of people without drinking water will cost $8 billion; while $20 billion would provide drinking water for everyone on Earth.In 2007, the LifeSaver bottle was tested by the London School of Hygiene & Tropical Medicine and the results found it to completely filter out all bacteria and viruses.The bottle's interchangeable filter can purify between 4,000 and 6,000 litres (1,050 to 1,585 gallons) before it stops working and needs to be replaced.