We just moved into a mid-century house in Ashland, OR. It's 3 beds, 2 baths, plus a small guest cottage with its own kitchen and bath with shower (and water heater). We're a young couple and will be renting out the cottage later this year, and hope to have kids soon, but we have low water usage habits so for now, we're not using a lot of water. It's near town but in a semi-rural area and on well water. The well is 70ft deep, tested last fall at 2.2gpm, feeds into a 1,000 gallon above-ground cistern, then has a separate pump to pressurize the house plumbing. We had a complete water test done in April before purchasing, and I can include the entire results here if necessary, but I read it all carefully and found that all contaminants which have an EPA limit are either not detected or very low - most are 1/10th or 1/100th of the EPA limit. So I'm not concerned about the safety of the water for drinking.

It's very hard water - 292ppm or 17GPG, and that is over the EPA limit of 250ppm, but doesn't pose any health problem. It does create lime scale anywhere it's heated, and contributes to a slightly mineral taste - not unlike some expensive European mineral water. But the water hardness is a topic for another thread, once we've fully moved in and have a break from installing new flooring.

Right now I'm just putting new cartridge filters in the well house. There are two of the 4.5 by 10 inch BB style filters, plumbed sequentially and directly after the pump, just before the water splits to run to the main house and guest cottage, both with the same 1 inch fittings as the rest of the plumbing in the well house. I'm trying to figure out what's a reasonable cartridge to install. Does it make any sense for one of them to be GAC or carbon block? I was thinking of having the Pentek dual gradient filters in both of them, running the DGD-7525 http://www.allfilters.com/sedimentfilters/10-big-blue/pentek-dgd-7525 in the first and the DGD-2501 http://www.allfilters.com/sedimentfilters/10-big-blue/pentek-dgd-2501 in the second. Theoretically, this would filter sediment down to 1 micron nominal with little danger of clogging the 1 micron final core filter. Both are rated for under 1psi drop at 10gpm, so it seems they shouldn't create much pressure drop. I haven't installed pressure gauges before and after the filters, but I'll get to that by the time they might need changing.

I know that 5 micron is often seen as overkill and a clog waiting to happen, and I'm not sure I need 1-micron level filtration, but here I have these two filter housings, so I should put them to use, and the DGD series looks like a good choice. Is there a way to know how much of what particle size of sediment exists in my water - without just popping in various filters and seeing how long till they fill up? Aside from the hardness of the water, I don't have any real complaints about using it, or concerns from the water test report, so I don't feel like filters other than simple sediment are necessary.

Also, there's a little Culligan under-sink filter in the kitchen, which supplies the kitchen sink and icemaker in the fridge. I just put a Culligan D20-A GAC cartridge in there. But we don't often drink or cook with the tap water - our previous house (on municipal water) had a possibility of lead and just tasted bad, so we got in the habit of filling a 7-gallon plastic water dispenser tank at the Glacier machines and using that for all our drinking and cooking needs, and we've continued to do that. We like the very neutral taste of the RO water (especially for coffee and tea), and Glacier machines are cheaper in the short term than getting a proper RO system under the sink.

So, given that I have these two filter housings for the whole house, what cartridges should I use?