You have installed leaf guards, a first flush diverter, a multi-stage sediment array, and a UV sterilizer. By all accounts, your water should be prestine. But how do you know? When dealing with your family's health and drinking water, assumptions are dangerous. Water Testing is the only definitive way to verify that your filtration system is functioning as designed.
Why Test Rainwater?
If you live in a city, the municipality tests the water hundreds of times a day. If you harvest your own water, you are the municipality. Testing is crucial for two main reasons:
- Establishing a Baseline: Testing water directly out of the storage tank (before filtration) tells you exactly what contaminants you are fighting. This allows you to design a targeted filtration array rather than guessing.
- Verifying Filter Efficacy: Testing the water at the tap (after filtration) proves that your UV light is actually killing pathogens and your carbon filter is actually removing chemicals.
What Should You Test For?
For a standard residential rainwater system, you don't need a comprehensive 200-point EPA analysis. Focus on the most critical biological and chemical markers:
1. Microbiological Pathogens (Crucial)
This is the most important test for any drinking water system. You must test for Coliform Bacteria and E. coli. The presence of these bacteria indicates that feces (usually from birds, squirrels, or raccoons on the roof) has contaminated the water supply. If these are present at the tap, your UV sterilizer or chlorination system has failed.
2. pH Level
Rainwater is naturally slightly acidic (usually around pH 5.5 to 6.5). While slightly acidic water is fine to drink, it can aggressively corrode copper plumbing and brass fixtures in your home, leading to pinhole leaks over time. Knowing your pH allows you to decide if you need a calcite neutralizer cartridge.
3. Heavy Metals (Screeing)
It is wise to test for Lead and Copper. If you live near an industrial area or an airport, a test for Zinc and Cadmium is also recommended. If these levels are elevated, a Reverse Osmosis system may be necessary.
How to Test
There are generally two approaches to water testing:
- At-Home Test Strips: These are cheap, immediate, and available at any hardware store. They are great for checking pH, hardness, and free chlorine levels. However, they are generally not accurate or sensitive enough for reliable pathogen testing.
- Certified Laboratory Testing: This is the gold standard. You order a kit online, fill a sterile vial with your tap water, and mail it to a lab. A few days later, you receive a highly detailed, professional analysis. For peace of mind regarding bacteria and heavy metals, lab testing is the only responsible choice.
Conclusion
At a minimum, anyone drinking harvested rainwater should send a sample to a certified lab once a year, preferably in the spring or after a period of heavy rain when the tank is full. The $50 to $100 spent on a test is a small price to pay for the absolute certainty that your water is safe.