Uncle Tilo's Guide to The Dual-Filter System for Effective Rainwater Filtration

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1. The First Stage: Sediment Filtration
   The primary filter in your system should aim to remove the bulk of the sediment from the water. Uncle Tilo suggests using a 20-micron polyspun filter for this task. Polyspun filters are exceptional at capturing sediment, ensuring that the bulk of particles are removed before the water moves on to the next stage of purification. These filters tend to require replacement after about three months for smaller units and six months for larger "big blue" units, depending on the quality of your system and the volume of water processed.

2. The Second Stage: Activated Carbon Block (ACB) Filtration
   Uncle Tilo recommends a 5-micron Activated Carbon Block (ACB) unit for the secondary filter. This type of filter is particularly effective if you're working with just one filter housing. ACB filters excel at removing chemicals and any remaining fine sediment, preparing the water perfectly for any subsequent disinfection processes. This level of filtration not only purifies the water but is crucial for ensuring the effectiveness of any additional water disinfection unit.

Choosing the Right Sediment Filter
While several sediment filter options are available, not all are created equal. Let's explore the alternatives:

Polyspun Filters: The top recommendation for removing sediment is that these filters capture significant debris and last the longest before needing replacement. Using a polyspun filter with an ACB can extend the life of your carbon block, typically up to 6 months without issues.

Pleated Paper Filters: Pleated paper filters are commonly used in pool systems. They can be cleaned and reused. However, compared to polyspun filters, they tend to capture significantly less sediment before clogging.

String Filters: For use in suction lines before the water pump, string filters remove large debris without easily clogging. However, they are not suitable for fine filtration. If you pair a string filter with an ACB unit, expect the carbon block to clog frequently due to the string filter's larger pore size. 


Choosing the right filters for your rainwater harvesting system is crucial for ensuring the safety and quality of your water. Uncle Tilo's guide serves as a foundation for understanding the importance of filtration and the best practices to adopt. Remember, clean water is not just about taste and clarity; it's about health and sustainability. By following these guidelines, you can enjoy the benefits of rainwater harvesting with the assurance that your water is clean and safe for all household uses.