ไม้ดู / Burma Paduk
A large slab of this wood is traditionally placed at the bottom of a newly dug well. It helps filter the water. When the groundwater slowly infuses through the wood, it helps sweeten the water and add medicinal qualities.  
 
This is one of the illustrations created for 'Samun Phrai Thai' zine. The zine is made to document the knowledge of traditional Thai medicinal herbs before they became lost.
Buy the zine here>