@Keith
For the past three years I have collected and processed rain water collected from an 1800 sq. ft. roof for all of my water use (including potable water). The following details the how and why of my system. Admittedly, it may be that I go to extremes but since my roof collects everything from bird/rodent droppings to potential airborne pathogens, the extremes seem justified. If it matters, since I have been using my system, I have never enjoyed any illness (GI or otherwise).
Apart from the water source, I regard your and my water purification needs as identical once the water arrives at its storage tank: yours from your well, mine from a water farm consisting of 3, 3000 gallon pools. (I maintain my pool water a 1ppm chlorine, liquid bleach - NOT chlorine "shock" chemicals which GREATLY add to the hardness of the water). My pool water is filtered by the pool pumps - whose micron dimension I don't know, and don't care since I seek only to filter major particulates.
Once in my storage tank, I continue to maintain the chlorine level at 1ppm (minimize algae growth). From the storage tank, I pump my water to a 39-gallon pressure tank (I live alone). From there, I push the water through a 5μm sediment pre-filter (Whirlpool WHKF-GD05; 6 month capacity). This filter serves, exclusively, to extend the life/efficacy of the next filter. That next filter (in series) is a 2μm activated charcoal filter (Whirlpool WHEF-WHWC activated charcoal; 3 month capacity). Taken together, these two filters render the water clean, almost odorless, and almost tasteless. More importantly, they prepare the water for the next stage by removing any large (>2μm) particulates. I house these filters in Omni whole house filter containers; these types of filters are standard size and will fit any standard whole house filter container. Both these filters meet ANSI Standard 42. Being in series, they reduce the flow rate at the tap, which is not an issue for me.
I then pass my filtered water through a Sterilight SQ5-PA UV system. My system is rated at 5 gallons per minute, i.e., water drawn through the UV system should not exceed 5 gallons per minute in order for the system to effectively kill any pathogens in the water. Sterilight makes UV systems in any number of capacities. One way to calculate your needs is to measure how much water you draw at maximum usage - how many faucets are open, on average at any given time (dishwasher/laundry running, someone is taking a shower, flushing a toilet, etc., at the same time). The UV bulb must be constantly on and is rated for 9000 hours (one year). Their effectiveness is influenced by water particulates/hardness - thus my filtration efforts. If you have very hard water (say an artesian well), you might consider a water softener BEFORE the UV system. The UV issue with particulates is that, if plentiful, and if pathogens are "swimming" in the shadows caused by the particulates, insufficient UV light will reach them.
At this point, the water should certainly be safe in any respect. However, I go one step further. I divert all of my drinking/cooking water through a 0.5μm Omni, CB3 undersink carbon block filter which conforms to ANSI Standard 53 for the reduction of 98.60% of lead; 99.99% of cysts; 99.60% of volatile organic chemicals (VOCs, i.e., gasoline); 99.19% of asbestos; chloramine taste and odor; mercury; lindane; atrazine; MTBE. This water has a dedicated, single valve, goose-neck tap at my kitchen sink. I have a fancy gallon dispenser in my bathroom which I fill as needed. My primary purpose in the carbon block filter is its ability to remove ANY pathogenic spores, i.e., pathogenic spores are >0.5μm. This filter reduces the flow rate at the tap to a crawl (<1 gallon per minute) but for drinking or cooking water needs it is not an issue for me.
As I mentioned, it's probably overkill but given what could be on my roof, I now drink without concern - and, if my health is any indication, the system all but guarantees safe drinking water.
I have researched the topic extensively and, if you wish further or more detailed info, post back.
Monk
P.S. Just reread your post: you cannot effectively use the 0.5μm carbon block filter as a whole house filter: shower head pressures would be nil, washers/toilets would take forever to fill, etc., etc.
