We have a well in our new house that has elevated arsenic (0.020) and radon (15,700). The radon is really high, the arsenic is twice the acceptable limit.
We installed this unit and had a arsenic and radon test done after the install. Our arsenic went from 0.020 to 0.0001. Well less than the 0.010 acceptable limit. Most impressive is the radon results, from 15,700 down to <200. The acceptable limit ranges from 2,000 to 10,000 depending on the state.
Because we have a well, we already have low water pressure (42psi), which is on the low side of what is recommended for this unit but acceptable we added the optional permeate pump so our ice maker would work. Our ice maker requires 20psi and as far as I can guess we were getting around 10-15psi. If you have a water filter on the ice maker you can require as much as 40psi unless you put a bypass on it.
After installing the permeate pump not only has our ice maker been working, filling cups/bottles from the RO faucet is much faster. You can order pump directly from Amazon and get it for 50% of the price with free shipping.
Aquatec AQUATEC-ERP-1000 Permeate Pump
It is the same pump they sell from their website, and you can get the directions for the installation by contacting them. The pump comes with instructions, but they are generic and not optimal. Without the pump, the 4 gallon tank will only fill up to 1.9 gallons, and the output water pressure is considerably less.
I was originally looking at the RO 50 unit but opt'd for the RO 90 as you can use the larger cartridges and won't have to replace them as often.
I am considering replacing the 4 gallon tank with the 14 gallon tank. This would give us a larger reserve and more pressure. With the pump though, we have a 3.1 gallon reserve instead of 1.9 gallon without it, so I don't think we will run out.