One of the first things to take care of during the purchase of a new home in Australia is the installation of a rainwater harvesting system that’s not just efficient, but also compliant with BASIX requirements. One of the ways to make a system compliant with BASIX requirements is setting up a roof made of material suitable for rainwater harvesting. While most materials used as roofing nowadays are already suitable for a rainwater harvesting system, only a few are suitable for collecting rainwater that’s safe for consumption. These are:
Asphalt Shingle Roofs
The asphalt fibreglass shingle is the most commonly used material for roofing these days, so there’s a chance that the roof of your new home will be made of this material. With new asphalt shingles, you can expect water that contains a lot of DOCs or dissolved organic carbon, molecules that are found in all bodies of water. Generally, DOCs aren’t harmful, but once combined with chlorine, which is often used in disinfecting water, DOCs produce carcinogens, which are substances that cause cancer upon ingestion.
Fortunately, DOC concentration in water decreases a year after asphalt shingle roof installation. Unfortunately, as shingles age, the concentration of pollutants such as zinc, iron, and particulate matter in water increases.
Asphalt shingles are usually treated with moss-killing chemical, which can pollute collected water due to its copper and zinc content.
Asphalt roofs set up before 1980 are, of course, not suitable for rainwater harvesting. These do not only have a deteriorated appearance, they might contain asbestos, a carcinogenic substance.
Water that has flowed down from galvanized metal to rainwater tanks is expected to not have a lot of DOC and fecal bacteria content compared to water that has flowed from roofs made of other materials. This is obviously an advantage; the rain that can be harvested from galvanized metal roofs is expected to not have much in the way of micro-organisms and contaminants that can make people sick, and thus can be purified so it becomes safe to drink in just a short time.
Galvanized metal roofing has a zinc and alloy coating, which seals the metal to prevent it from rusting. Rusting causes a lot of iron to be introduced to the water.
The good thing about concrete roofing is the fact that it’s easy to clean, and since it’s easy to clean, you are assured that the rain that gets into the tank from this kind of roofing is ready for use. Watch out for algae and moss growth, though.
Like concrete roofing, this type of roofing material is suitable for use in rainwater harvesting, provided that you keep it clean. And like in the case of concrete roofing, algae and moss can grow on terracotta roofing too. With the latter, however, the growth of moss and algae is slower.
Often, terracotta roofing is cleaned by spraying it with chlorine. Let the chlorine dry out from the roof before using the rainwater harvesting system again.