Wood Shingle Types for Potable Rainwater Catchment

I'm in the process of designing a potable rainwater catchment system for a new build, and I'm trying to figure out what types of wood shingles are okay to use. Here's what I've heard so far:

(this is all word-of-mouth or found in internet searching, so I'm not sure how reliable this is!)
- the wood shingles should of course be untreated,
- but cedar is not okay because it leaches toxic oils for the first 3 years,
- and redwood, oak and chestnut aren't okay either because they leach tannin into the water

I'm hoping someone knows of some wood types that are good for potable rainwater catchment/storage?

- Ben

I don't know the answer, Ben, but I do know that redwood is used here in Hawaii for catchment tanks. Has been used for decades with no problems that I've heard of.

All of the woods that are suitably rot resistant are bound to have a little or a lot of those oils and tannins. Perhaps the water could be filtered or treated in some other way after gathering. I would prefer to drink rainwater from a plant covered green roof built with a fish safe EPDM liner.

I live where cedar is abundant but it's not something I would shingle with. It gets covered in moss and is prone to other problems in the wet environment where it grows. Cedar as a roofing material is actually better suited to places that have a hot summer and cold winter, since decay organisms on a roof in those conditions, are active for a very short amount of time each year. I saw some shakes in the Yukon that were a century old.

I'm really interested in knowing more about this, in particular about water catchment off Oak shingles.

This is also something I am interested in. I also wonder in what amount of tannins would leach in, as in the right amounts tannins are often considered healthy. For example green tea also contains tannins.

Rainwater off different roofs

This is a scientific study oif the effect oif different roof surfaces, they are interesting to read.

The part about Dissolved  Organic Carbon [DOC ]mixing with chlorine particularly.

The study also showed that rainwater from asphalt fiberglass shingle roofs and increasingly popular "green" roofs contain high levels of dissolved organic carbon (DOC).
Although other potential pollutants can be significantly lower on green roofs (turbidity and aluminum), the high DOCs are significant where these roofs would be used for potable rainwater collection.

And interesting study indeed, but unfortunately no mention of wooden roofs from what I can see. I have ordered the book "Essential rainwater harvesting" and there they briefly talk about wooden shingle roofs, saying that usually they are not used and cedar shakes can be poisonous but that well managed wooden roofs can deliver high quality water. Unfortunately I could not see any further information on that so far, but let's see if I can find any references resources once I have the book.

I could also find some studies that seem to talk about wooden roofs for rainwater catchment, but they are unfortunately either paid for or not in english:
- https://www.researchgate.net/publication/221746231_Quality_of_roof-harvested_rainwater_-_Comparison_of_different_roofing_materials
- https://www.researchgate.net/publication/349906397_Roof_runoff_contamination_a_review_on_pollutant_nature_material_leaching_and_deposition
- https://www.researchgate.net/publication/263363138_The_Effect_of_Roofing_Materials_for_Using_Harvested_Rainwater

But looking at the latest two, it is possible to look at the graphs and from what I can tell they seem to suggest that wooden roofs are fine, as long as mosses are being kept off it.

Also just found this document which seems to collect some different studies that also look at wooden shingle roofs: https://repository.lib.ncsu.edu/bitstream/handle/1840.4/8170/1_NC-WRRI-425.pdf?sequence=2&isAllowed=y - I have not looked at it in detail but at a first glance it does seem that wooden shingles might not, by itself, produce the highest quality water but still within range for drinking quality if mantained correctly.