WALKERS who set out with supplies of distilled water - rather than mineral water - are risking sickness and possibly death, an expert doctor warns. Dr Ho Hiu-fai, a medical adviser on the gruelling annual Trailwalker race and doctor at the Queen Elizabeth Hospital's accident and emergency department, said muscle fatigue caused by salt loss could have dire consequences. His warning follows the recent death of three hikers and the illness of many others in the heatwave that came ahead of Typhoon York this month. 'People lose water and salt through sweating and if you drink distilled water, it will just replace the water,' Dr Ho said. 'When you lose too much salt you can have a lot of problems with your muscles and it's hard to maintain their normal function. 'You can have heat exhaustion, heatstroke, and because of your tiredness you might get into trouble. 'Your alertness might decrease and you have an accident, or you might not be able to finish the walk.' Dr Ho said that in extreme cases, loss of body salts could cause the heart to start beating irregularly and lead to convulsions, though this was unlikely on a walk. A 59-year-old hiker was found dead in Sai Kung West Country Park two weeks ago after her husband left her to rest during a four-hour walk. The previous day, two men - aged 31 and 38 - died on separate hiking trips, one on the MacLehose trail in Sai Kung and the other on a hike to Tai Po. Six other hikers were taken to hospital that day. Heatstroke is suspected to have caused the three deaths, but an official announcement has not yet been made. Mineral water giant Perrier Vittel estimates Hong Kong people drink an average of 32 litres of bottled water a year. Much of that is believed to be distilled water, which tends to be cheaper than mineral water and is popular in the SAR despite being sold only for car batteries and steam irons in many other countries. A Health Department spokesman said hikers could eat to top up their mineral levels if they had distilled water rather than mineral water. 'If you go out on a very hot day and are perspiring profusely, the body might lack minerals and if you're drinking distilled water, it's advisable to have food also,' he said. Numerous teams are now training for the 100km Trailwalker, to begin on November 12, and the present warm weather is luring amateur walkers on to country park trails. Dr Ho said walkers should make sure they were well prepared before heading out by ensuring they were fit enough to complete the course, eating a balanced diet and taking adequate drinks. 'Mineral water contains some of the salts you lose through sweating and sports drinks usually contain balanced electrolyte solutions,' he said. 'At the checkpoints on the Trailwalker, we have electrolyte powder to add to water.' Groups should stick together and never leave anyone behind. As a last resort, distilled water could prevent dehydration and was 'better than nothing, but it's not ideal', Dr Ho said.