Historically, heat waves have resulted in more Australian deaths than any other natural hazard and continue to present challenges to the health and emergency management sectors. While people experiencing homelessness are particularly vulnerable to adverse effects of heat waves, little research has been reported about their hot weather experiences. This paper reports findings from interviews with 48 homeless people sleeping rough in Adelaide CBD on very hot days. While the majority reported drinking a litre or more of water in the previous 24 hours, 79% reported experiencing one or more heat stress symptoms. The research highlights that the protective actions people sleeping rough can take during hot weather are limited by their circumstances and may not be sufficient to prevent dehydration and heat stress. The levels of dehydration and heat stress symptoms suggest that immediate responses could include making drinking water more readily available. It may be helpful to provide information which highlights heat stress symptoms including indicators of dehydration. The role of outreach in providing connections, support and advice is most likely to ameliorate the risk of heat stress. However, the long-term response to protect people from heat stress is access to housing.