The Terminator is back – and heading to Cape Town to talk about Day Zero.Arnold Schwarzenegger – movie star, former California governor and now a climate change activist – will be the keynote speaker at the W12 Future of Water conference to be held in May 2019.While most people know Schwarzenegger as a silver screen action hero who later turned politician, he has become something of an environmental crusader, particularly about climate change.Although Republican, he is a strong supporter of taking climate change action and uses his fame to draw attention to what has been described as the greatest threat facing humankind.The conference will focus not only on Cape Town's water crisis, and how the city successfully dodged the Day Zero bullet, but also on the rest of the "Big 12" – major water-stressed cities that may soon be facing similar water crises: Sao Paulo, Bangalore, Beijing, Cairo, Jakarta, Moscow, Istanbul, Mexico City, London, Tokyo and Miami.Stakeholders from all these cities are expected to attend and one of the aims is to share Cape Town's Day Zero experiences and show how ordinary people can pull together to avert a crisis.The three-day event will be the first to bring together people from the 12 major cities where water demand is likely to exceed supply within the next few years.'Scared people into taking action'The W12 conference with the big-name drawcard grew out of small beginnings.It started with Shelley Humphreys of Vredehoek, who ran a PR company. She knew about the drought, but did not realise the severity of Cape Town's water crisis until late January when her 10-year-old daughter came home and said the taps were going to be turned off in school toilets."I think for me that was the moment when I realised the situation was serious."Out of that grew Save our Schools, a non-profit organisation Humphreys founded in March.In August, Unesco (United Nations Educational, Scientific and Cultural Organisation) accepted Save our Schools as a non-profit partner in the water sector.Humphreys believes the City of Cape Town's Day Zero campaign was highly effective."It made world news and it scared people into taking action. People were saying: 'Okay, this really is a crisis', and there were fights in the supermarket over bottled water and people started hoarding," Humphreys said."But the great thing it did was to force people to change. It forced people to understand the value of water and how much they used. Suddenly everyone knew how much water their washing machine took and how much it took to flush the loo."Yes, it had an effect on the economy and tourism, but I believe it effected a behaviour change regarding water that will never go away."Transfer of knowledgeShe and her business partner René Frank forged partnerships with businesses and other organisations and Save Our Schools expanded. To date, it has provided 17 schools and 25 000 pupils from disadvantaged areas with water. Some of the water is used to keep school food gardens alive.Frank describes the W12 conference as a platform for the transfer of knowledge about the Cape Town situation to the cities that are facing the real prospect of running out of water."We need to bring all these people together to share that information, to say: 'This is what we did in Cape Town, together, as citizens.'"Arnie Schwarzenegger is using his fame as a movie star to say: 'We have a serious issue,' and also to say: 'I'll be helping'," Frank said.Humphreys believes it is important to tell the other cities that what Cape Town did well, was to make the battle against the worst drought on record, citizen driven.It will give them tips on what to do and keep them engaged.SOS is organising the W12 conference with Wesgro, the official trade and investment agency of the Western Cape government.Wesgro CEO Tim Harris said: "Never before have conferences of this nature been more important globally, with drought, as a consequence of climate change, becoming a global phenomenon."Unesco says drought, a complex natural hazard with significant socio-economic and environmental impacts, causes more deaths, and displaces more people than any other natural disaster.