The Lifesystems Chlorine Dioxide Tablets and effective and very easy to use. Simply add 1 tablet per litre to relatively clear and debris free water. If the water is very cold or if Giardia or Cryptosporidium is suspected, add 2 tablets per litre of water. Swirl gently and wait for at least 10 minutes before drinking, or 30 minutes is two tablets have been used. FeaturesContains 30 foil sealed tablets - will treat up to 30 litres of water.Part of the DofE Award recommended kit which features on the DofE Expedition Kit ListKills bacteria, viruses and cysts in water - including Giardia and Cryptosporidium.No after taste - pleasant to drink.Weight: 40g