Every 6 months may be a bit of overkill. I believe they use standard 20"x4.5" filters. I have a dual canister 20" x 4.5" system with a 5 micron pleated sediment filter and a 5 micron carbon block filter. The main purpose of the sediment filter is to extend the life of the carbon block filter by removing any sediment that would clog the carbon block filter. The pleated sediment filter can be hosed off and reused. Given the chlorine level in The Villages, the amount of water we use daily, and the chlorine absorption specs of the carbon block filter, I replace the carbon block filter every 2 years. At that time, I hose off the sediment filter but it is always pretty clean. I do replace the pleated sediment filter after 6 years ( two hose offs). I have tested the water at 2 years for chlorine leakage and found none so 2 year replacements on the carbon block filter is fine.

It really depends on where you live in the Villages. Some may need a change once a year. I have a friend who does what you do but goes every 5 years no problem. I have another friend who's trying to go 10 years.

The chlorine level in The Villages potable water is advertised. Carbon block filters are spec'd to handle a specific amount of chlorine. How much potable water you use is easy to determine from your water bill. The calculation of how often to change the carbon block filter is a simple calculation. 5 years or 10 years between filter changes, unless you use very little water, if almost certainly outside the spec for a 20"x4.5" carbon block filter. However, people are free to do whatever they want, regardless of whether it makes any sense.

Nova recommends changing the filters every 26,000 gallons. I asked how they determined that figure and the answer was basically that they are dirty enough at that point to be icky and inefficient.

If someone has a better MEASURABLE metric, please share. Saying 2 years or 5 years is meaningless since every household has different usage needs. A home of 4 people that lives in TV year around is vastly different than a single person that snowbirds.

The 26,000 gallons that Nova came up with is their measurement given what the filters are rated for and the quality of the water here in the Villages. If we had well water, the recommendation would be different for example.

That said, you are right. Depending on how much water you use will depend on when to change the filters. So, what you need to consider is first, how fast is the sediment filter getting dirty in your home since sediment varies in different areas of the Villages? Most here in the Villages are not going to open their filters to check. You can't clean the carbon filter so you can measure your water to see when you start to see chlorine and then change them. Or you can just say I'll change them once a year and not worry about the $125 or whatever Nova charges. Remember, no matter what anyone tells you, these filters are very heavy when filled with water so if you get the tool and try to change the filters yourself, be very careful because when you unscrew them, they are going to drop off the mount like a rock and you can get hurt.

The question you need to ask yourself is for $125 or whatever Nova charges, is that money worth the trouble of trying to test and or guess when you need to change your filters which may vary since the sediment and chlorine levels change a lot here in the Villages? If not, then just change them yourself or have Nova do it once a year. If you find the filters are clean after a year, do it every 1 1/2 or 2 years if you want for example. Here in Osceola Hills mine and my neighbor's filters looked mildly dirty after a year for a couple of years then this year after a year they were very bad. I tried to clean mine and it was a mess they were so dirty so I just changed them.

Based on the specs of the carbon block filters I use and the chlorine levels in The Villages potable water, the carbon block filters, that I use, are good for approximately 40,000 gallons. This is essentially 2 years, rounding up a bit, for the amount of water we use. The 5 micron pleated sediment filter, in front of the carbon block filter, can be hosed off and is typically pretty clean at 2 years. I suspect the amount of sediment in the potable water in The Villages varies somewhat; our water is very clean now but it was pretty dirty for the first 2 years we were in the house (new construction area). I do occasionally measure the chlorine level to check and this interval has been fine. YMMV.

Guessing is silly. If you agree that 26,000 gallons is reasonable, simply monitor your monthly water bill. I track mine on a spreadsheet that adds and totals cumulative usage. When I get to 26,000 I buy new filters and swap them out myself. Yes they are heavy. Put an upside down bucket or similar with a folded towel underneath the canister before you unscrew. This is not a difficult job for anyone with even a minimal amount of handiness, and you will save some $$$.