The DMG lays out rules for foraging, and lists the DCs as such:

\begin{array}{ll} \textbf{DC} & \textbf{Food and Water Availability}\\ 10 & \text{Abundant food and water sources}\\ 15 & \text{Limited food and water sources}\\ 20 & \text{Very little food and water sources}\\ \end{array}

In the Tomb of Annihilation adventure, It is stated that drinkable water is only available by harvesting rain water. All other water is deemed unfit to drink unless it is boiled first.

So, how do I handle foraging for food and water in this case? It seems like water is abundant, but undrinkable. However, can the character forage during the day and boil the water in camp at night? Is there any official ruling on foraging in Tomb of Annihilation?

Barring any official ruling, has anyone run this adventure with foraging? If so, how did you incorporate the foraging system given in the DMG?