I'm not a plumber, but I am an engineer. I've mostly worked in dirty water since school, but I did mostly clean water then.

THMs are trihalomethanes, and they are a class of chemicals called disinfection byproducts. Basically, any chemical that's added to disinfect drinking water reacts with naturally-occurring organic matter in the water (think the dissolved remnants of stuff like leaves, algae) to yield tiny tiny concentrations of these chemicals. The main thing that affects how much THMs form is the time the water sits in the pipe and storage tanks between the plant and the point of use.

The last I paid attention to it, we know that THMs in massive quantities are carcinogenic in the lab. The rules your utility follows are an attempt to extrapolate from what we know to protect the public against exposure to tiny amounts over a long time. FWIW, my recollection is that the prime exposure path is actually via steam inhaled in the shower.

The good news is that a carbon filter is a great way to remove the residual disinfectant (chlorine or chloramines), THMs, and other organic chemicals (VOCs- volatile organic compounds). And it takes care of the main complaint that leads to getting a filter in the first place- that the water doesn't taste good.

I'm not a big RO proponent for home use. Unless you have someone who's immunocompromised or have a lot of dissolved solids (due to softening or from being in a coastal area that has saltwater intrusion), I think it's overkill. And it's expensive, has expensive consumables, and wastes a lot of water to produce a little. There are always exceptions, but that's my general feeling.

Your faucet should be fine if you get a carbon filter. The problem with RO is that it makes the water more likely to dissolve metals it comes in contact with. Water that's just carbon filtered is still buffered to prevent this.

I don't think there's a problem with going generic. The issue with the proprietary systems is that they lock you into their replacement cartridges and those are usually at a premium. You can get housings and filters much more cheaply. One tradeoff that comes to mind is that the proprietary setups may have an easier arrangement to replace filters. Otherwise, you have to be a bit of a plumber yourself to put together the housings, valves, fittings, etc.

The simplest setup would be a single filter. This is like what’s in most fridge and point of use filters. There are combination cartridges that remove lead, cysts (tiny pathogen eggs that are very hard to kill) and have carbon for chlorine, THMs, VOCs. A step up would be a multistage system that adds a sediment filter and maybe a second stage of carbon. This is what we have in the water coolers at my office, which run on tap water instead of jugs.

As for the pool, the color problem after the tornadoes is a bit of a stumper. Probably not something that’s going to happen often. And I don’t know if a simple sediment filter would take care of it. Otherwise, there’s a whole ‘nother set of chemistry going on in your pool, and frankly I wouldn’t worry about filtering what you fill the pool with unless it looks bad. Not to mention that a carbon filter that sits around unused tends to have some of the stuff it’s collected re-dissolve into the water sitting there.

Last but not least, how well any of this works is dependent on how good a job of maintenance you do. Timely filter replacement is critical. Either based on a conservative time schedule or testing the filtered water for chlorine breakthrough. A buddy who does water treatment for Coke’s bottlers reminded me lately that it’s also a good idea to flush the system with unfiltered tap water when you replace filters. This puts some chlorinated water through so that you kill anything that’s grown in the housing and tube/pipes. Not something I logistically can do with my fridge filter but a very good idea.

McMaster Carr (industrial supply house) has always been a good reference to get an idea of cost, but Amazon also seems to carry most everything these days too. I’d look there and look at some of the pre-built systems to decide what works best for you.

Thank you, Thull. That was a great explanation of everything.

Our water dept will switch to a different rural water district since our current one can't get rid of the high amounts of THMs. It will take another year though until we have better water.

The only reason to filter the pool water is because of the brown water we get after big rains. The entire lake turns muddy red. You can actually see the line of red water where the river flows in the lake. We spent a lot of time and money on chemicals because of the brown water. Plus we didn't even get to use the pool in May, June, or July. The lake is settling now, but I still get some brown water occasionally. The filter might help with that. I will probably try a sediment filter like you suggested.

I like the idea of a carbon filter, then a filter for lead, then a second filter. So maybe a 3 stage filter system.

Thanks again for a great explanation. Peke

You're welcome. Just remember to put the sediment filter first if you do multiple filters in series.

I'm really surprised that you get color like that in your water, where it sounds like it's essentially mud. Typically, the first step in water treatment (after getting random trash out) is to add a chemical called a coagulant (alum is the most common) and then get the solids to agglomerate and settle out. Between that and a later sand filtration step, you'd get out any color/solids. Some systems may not have to do both solids-removal steps (NYC is one, IIRC due to very-clean source water from way upstate), but it seems like the stuff you're seeing would be evidence that it's needed.

I have been told that our water comes from the lake in front of our house before it is treated. So when the lake is brown our water looks pale brown. Peke

Peke,

If your house was built after 1982 you won't have any lead issues. If you have galvanized or plastic plumbing you won't either.

Thull gave a good explaination of TTHM and VOC's but 99.99% of the population won't ever come down with anything that DPB's are alleged to cause.

Tastes are usually a problem with stale water in your plumbing. Most folks take a draw straight from the faucet or refridgerator water dispenser which can sometime sit for hours before being used. Water also absorbs the plastic flavor in water lines for ice makers.

As for the dirty water from the lake, is your water system surface water or ground water? There is a better chance that the red water is coming from an iron main or from your owm pipes.