To get the achievement Voice of Flowing Water in Genshin Impact, you must complete the entire collection of books, Heart of the Spring, which consists of four volumes. In addition to the achievement, you will receive 5 source stones as a reward.
Volume I
The first book is located east of Kellingen. If you can see the mill already, keep to the left. There is a barrel of flowers next to one of the houses. Stand in front of the barrel and you will see a spark that signals an item. Interact with him to get the first volume in the book series.
Volume II
Travel to Mondsstadt and use the first staircase to the city. Keep Left. On the left you will see a table with chairs on which the book lies.
Volume III
Go to the Ordo Favonius headquarters building, which is also located in Mondstadt. There is a door on the left - open it and enter the room. Look to the right. There is a bookshelf between the two sofas, above which there is a large coat of arms. Stand in front of the bookshelf and interact with it to get the third volume.
Volume IV
Enter the Dawn Distillery. Approach Adelinde and examine the shelf behind her. You will see a candlestick and several books on and around the shelf. Interact with the spot next to the candlestick for the fourth and final book.
The first volume is not to the left of the guild, but to the left of the Ordo Favonius headquarters