Biodegradable bamboo charcoal water filters. Reusable, then compostable and zero waste. Suitable for a 1 litre jug of water. A pack of 4, in a reusable natural cotton bag. Use approx: 1 litre jug = 3 - 4 pieces; 2 litre jug = 6 - 8 pieces. Boil for 10 mins in a pan of water to sterilise & allow to cool and dry, Place in a jug and fill with tap water (charcoal may float when new but it will tend to sink after a week or so of use). Leave for 8 hours or more for best results. You can leave it in the fridge to chill if you like. It's then ready to drink. Re-sterilise once a week. Replace with new charcoal after 2 months approx.