Rainwater collection is genuinely common out here. On acreage around Kerrville, Comfort, Spring Branch and the western edge of Kendall County, a lot of properties either supplement their well with collected rainwater or run on it entirely.
If your roof is your water supply, the roofing conversation changes completely.
Why metal is the standard for collection
Metal is the default collection surface for several converging reasons:
- It sheds cleanly. Smooth panels move water fast with minimal surface contact time.
- It doesn't shed granules. Asphalt shingles continuously release mineral granules — that's how they age. Those granules end up in your tank.
- Less organic growth. Smooth, hot metal is an inhospitable surface for the algae and moss that can colonize other roofing.
- Inert coatings are available. Quality PVDF finishes are stable and well-characterized.
- Long service life. Replacing a collection roof means dealing with your water supply during the work. Doing it once every 50 years rather than every 20 matters.
Can you collect off an asphalt shingle roof?
For non-potable use — irrigation, livestock, topping off a pond — plenty of people do. For potable use, it's generally discouraged. Granule shedding, the petroleum base of the shingle itself, and the algae-resistant additives in some products all argue against it.
If you're currently collecting off shingles for household use, that's worth a conversation with whoever handles your water testing.
Coatings: the question to actually ask
Not all metal roofing finishes are equivalent for collection. The question to ask your roofer or supplier is specific: is this panel's coating appropriate for potable rainwater collection, and can you point me to the manufacturer's documentation on it?
Quality PVDF/Kynar finishes are the common answer in this market. Avoid older or unknown coatings, and be cautious about field-applied coatings and sealants that weren't specified for collection use.
Also worth asking about: the fasteners, flashing and sealants, since those are in the water path too.
What the rest of the system needs
The roof is one component. A well-built Hill Country collection system also includes:
- Gutter screening to keep leaves, oak catkins and cedar debris out of the conveyance
- A first-flush diverter that discards the initial volume of each rain event, which carries most of the accumulated dust, pollen and bird droppings off the roof
- Proper conveyance materials rated for potable water
- Filtration and treatment sized to the use
- Tank design that keeps light out and keeps the water cool
Hill Country limestone dust and cedar pollen make the first-flush component more important here than in other regions. During cedar season the volume of organic material landing on a roof is substantial.
Roof design details that help
- Simple roof geometry. Fewer valleys and penetrations means less debris accumulation and less contamination risk.
- Adequate pitch. Water moving fast spends less time in contact with the surface.
- Generous gutter sizing. Six-inch gutters with sufficient downspouts capture far more of a high-intensity Hill Country rain event than five-inch. Overflow is lost water.
- Avoid overhanging trees where practical — they're the main source of organic loading.
Replacing a collection roof
If you're replacing a roof that feeds a collection system, plan the water side too. You'll want to isolate the tank during the work, and you'll want the system flushed and the first several rain events diverted after the new roof goes on, since fresh panels shed manufacturing residues initially.
We work on collection properties
Metal roofing across Kerrville, Comfort, Spring Branch, Bulverde and the rural Hill Country, including properties running on collected rainwater. Get a free assessment or call (210) 245-4125.
