For Version 10, the recommended flow rate is 0.4 L/min (measured when the reservoir is full to the top).
CAWST has found that this flow rate can be achieved if the sand is prepared using the 0.7 mm (0.028") opening size screen to remove all coarse sand and then washed as many times as necessary to remove excess fine sand.
Your sand and gravel sources may vary so the number of times that you wash the sand will have to be adjusted periodically. After some time you should develop the ability to know when the sand has been adequately washed just by looking at the wash water in your container. It will take practice to know how many times you will need to wash the sand.
For the final test of the sand, install a biosand filter on site using your filtration sand and gravel and test the flow rate. The flow rate should be 0.4 L/minute when the filter is installed.
