MORE About Hawai`i’s Acid Rain for Catchment Tanks

BY: Trisha Macomber, MPH, UH College of Tropical Agriculture & Human Resources, Cooperative Extension Services

Because many questions have come up lately about the pH (a measure of acidity or alkalinity) in our catchment systems, we want to give you more detail on how acid rain can affect you through catchment water.

Different locations may require different treatment

The pH scale measures how acidic or basic something is. This logarithmic scale goes from 0-14. Numbers below 7 are considered acidic and above 7 are basic. Seven is neutral. Rain usually has a pH in the mid to high 5’s. Less than 5.6 is considered “acid rain.” On the mainland, acid rain is usually associated with pollution from burning fossil fuels that release excessive nitrogen oxides into the atmosphere. In Hawai`i, the biggest cause of acid rain is from our volcanoes, which release sulfur dioxides and trioxides into the air. These oxides, in a series of reactions in the atmosphere, combine with water molecules and form dilute acids which return to earth as acid rain. Usually Hawai`i’s acid rain contains sulfuric acid where other types of air pollution can create nitric acid.

Why does acid rain matter?

Normally rocks, soil and vegetation act as buffers and neutralize the acid. If the pH is really low, it can damage delicate vegetation and cause ecological damage. In rainwater catchment systems, acid rain can be a problem because it can leach metals and other surface and tank coatings and deposit them into the water. This is a particular problem in older homes—typically built before 1979—where roofs might have lead paint, nails, flashings and solder.

Is acid rain a health hazard?

Drinking acidic rainwater isn’t normally a problem. In fact, we drink a lot of acidic drinks and food. However, excessive acid could affect your teeth. Just like drinking soda pop or sucking on lemons, if you constantly expose your teeth to acid conditions, their protective enamel coating will be compromised.

Our biggest concern about drinking acidic rainwater is when heavy metals and other leached materials get into the water. A very common problem is when copper from water pipes make blue/green stains on our sinks and tubs. Sometimes severe leaching will cause pipes to leak.

Having some copper in our water is not necessarily a health hazard because our bodies need some copper. Many people’s diets in the US are deficient in copper and vitamin C inhibits the body’s intake of copper. However, if you suspect your copper levels are high, especially if you can taste the copper in your water, it may be too high and you should get your water tested.

Where to get your water tested for copper and lead

The cost of copper and lead water testing is partially subsidized by the Department of Health’s Safe Drinking Water Branch. On the island of Hawaii, call 933-0401 to make arrangements. You can also do inexpensive testing for lead and copper through the UH College of Tropical Agriculture and Human Resources, however these laboratories are not certified for drinking water, so if you use them, you should only use the results as a reference (for example, your levels are high or low), rather than focusing on a specific number.

Charcoal or carbon filters can also remove heavy metals

You can add filters made from charcoal or carbon blocks to remove lead, copper and other similar contaminants from the water. These filters should have a list of what contaminants they remove on the outside packaging. We also recommend that the product you buy contain an NSF International seal, which verifies the manufacturer’s claims.

How to get pH testing

If you want to test the pH of your water, you can buy simple pH test strips from chemical supply stores or from the UH CTAHR Hilo office. PH testing kits are also available from swimming pool supply stores and some hardware stores. In addition, there are local water laboratories that can do pH testing, if you prefer to bring a water sample to a lab, call the lab first to learn how to collect your water appropriately.

How to raise the pH levels in your catchment tank

If you need to raise the pH in your water, dissolve about 1-2 boxes of sodium bicarbonate (baking soda) in a bucket of water and add it to the tank every 2-4 weeks. You may need more, depending on the acidity of your water and size of your tank. Too much baking soda will make your water start to feel very soft or slimy. The baking soda also adds salt into your water, just like commercial water softeners do, and may be a problem for people on restricted salt diets.

Another product you can add is food-grade calcium carbonate granules, which are available from chemical supply companies and some local suppliers. Large solids of calcium carbonate, like limestone rocks, are not effective because the sulfur coats the surfaces and does not wash off. With limestone granules, the surface area is much larger, so they will work longer.

Concrete hollow building blocks or tiles are not effective as their surface gets coated quickly and they are not food-grade, so they should not be added to catchment water.

For more information, please contact Trisha Macomber, MPH, UH College of Tropical Agriculture & Human Resources, Cooperative Extension Services, 981-5199 or send and e-mail to: macomber@hawaii.edu.

https://www.ctahr.hawaii.edu/hawaiirain/more-vog.html