MaxBlack said:
What is curious to me is that there is very little available (at least on the Internet) in the way of hard information on filtration and purification systems beyond water-well types (e.g. spring or lake or in my case Rainwater collection). There are a lot of individual gizmos out there, but not as much in the way of "puddle-to-sink" advice. Maybe someday Bob NH will add to his "hobby" business the sale of "how-to" manuals for the systems he puts together... Or maybe I will do it as I will become myself an expert before too long (or die trying)!
I can explain the system here in a few paragraphs. The actual hardware depends on your situation.
The principle is to filter the water to get out anything that is filterable, and to disinfect to take care of anything the filter won't catch.
The first stage is to pump the water through the best cotton filter I can get. The manufacturer says it is 0.5 micron! Don't believe a word of that. I tested the "0.5 micron filter" with a certified Met-One particle counter and found that it removed about 99% of 5 micron particles. For those who know logarithms, that is known as 2-log reduction. That was sufficient to be allowed credit for 1.5 log reduction, or 97% removal.
Then I needed to provide disinfection to provide another 1.5 log inactivation of giardia to get a total of 3-log (99.9%) removal or inactivation of giardia. That requires a contact tank (a big polyethylene tank) that provides 30 to 45 minutes of contact time at typical temperature, pH, and chlorine content. There are baffles in the tank to prevent short-circuiting of the flow.
Water is pumped from the contact tank into the distrubution system; usually one or more hydropneumatic tanks. Systems usually have the tanks in place; some about 50 years old. I have seen more than a few old riveted tanks still being used. The largest was about 5000 gallons. No bladder tanks available in that size.
In the past couple of years, I have started adding the Harmsco 1-micron-absolute filters as a second stage. Although that filter has been demonstrated to remove 99.9% or more of giardia-size particles (about 5 microns) the credit for filtration is limited to 2.5 Log (99.7% removal) and disinfection is used to achieve the total 3.0 log required. With the 1-micron-absolute filters the required contact time is on the order of 10 to 15 minutes.
Sodium hypochlorite is added by a positive displacement pump that runs at the same time as the first stage water pump. Most systems use household bleach because there are no OSHA issues handling it, as there would be with commercial 15% sodium hypochlorite.
The first stage filters are operated at about 0.5 GPM per equivalent 10" length, which is 1/10 to 1/6 what most manufacturers rate them for flow. That results in a lifetime of 10,000 to 15,000 gallons per 10" unit when filtering water from small lakes without too much algae. Most seasonal places operate all summer with one set of filters. I designed and build my own filter housings to get lots of area at low cost for the housings.
I build a custom control panel for each system using relay logic that is easy for the users to maintain. All controls are automatic so the only operator action is to make the required daily measurements and keep the chlorine feed tank supplied. They also need to watch the pressure gauges to know when to change the filter cartridges.
Regulations require daily tests of chlorine content, pH, temperature, turbidity, and water usage, and a calculation of disinfection effectiveness. That would not be required for an individual system.
The disinfection kills all bacteria and viruses. The filters may remove some bacteria but I don't count on that. Nobody ever has a problem. Nobody has ever failed the required coliform test and no "boil water" orders on any of my systems.
Water sources include lakes and ponds, shallow wells, and roof drainage.
I drink the water from any system that I install.
I usually use submersible pumps because they are the most versatile for getting proper head and flow.
I see a lot of systems where "professionals" have installed big 5 HP or greater centrifugal pumps to develop pressure when all that is needed for the flow is a 1.5 HP submersible matched to the system. Many have operating problems with their previous systems that I solve with the installation of the new systems.
Nobody has ever had to add staff to operate the system, although the state does now require a "very small system operator" license. The usual process if for the maintenance person to study for and take the test.
Adapting the system to home use requires only scaling down the components. Most of the material, except the filters and pumps, is available from HD or Grainger. A home user would not bother with a turbidity meter but must have a chlorine test kit.