It can be difficult to suggest the best system because there are two big unknowns: the quality of the water you will be processing, and your preferences for degree of purity. With an unlimited budget, you can obtain whatever level of purity you’d like, but most people don’t have that available. So, it comes down to what you’d like and what you’re willing to tolerate. Most people choose a system that works well but is not terribly expensive. Let’s look at the whys and wherefores of water purification.
There are two main functions of water filters, removing particulates (sediment) and removing taste and odor contaminants. The former is done by forcing the water through a medium with very small pores such that the particles are physically trapped in the medium. The latter is done by a process called adsorption in which the contaminants “stick” to a receptive medium, usually activated carbon. Both of these functions can be combined into a single filter element, but for best efficiency and potentially, the lowest cost, separate filters are the best.
Generally, one sediment filter (which can remove particles down to 1 micron in size) and one carbon filter (the best of which can remove particles as small as 0.5 micron) are used in combination. At best, you can remove cysts and most noticeable contaminants from your water with this setup. To remove more, you’ll have to use a finer filter, like a ceramic that takes out particles down to about 0.5 microns absolute, which includes most bacteria. The cost is significantly reduced flow and pressure.
Be aware that filters have limitations. They cannot remove totally dissolved materials easily, although we do have some filters that work on some minerals. Calcium and magnesium are what cause water to be hard, and filters are not the best for removing them. Water softeners and reverse osmosis (RO) are better suited for that job. Other dissolved minerals and compounds, such as lead, heavy metals, iron, arsenic, fluorides, and nitrates (to name but a few), can be removed with special filters.
For your situation, I would recommend a dual or triple canister filter setup. If you have room in your wet bay or other location, you could permanently mount the filter canisters, which would minimize the chance of theft but if not, you could set the canisters up outside. They can be installed or used in any configuration that works best for you, and they do not have to remain upright, unless a loose media cartridge is chosen. You should try to protect them from the elements, though, particularly the sun. With a three canister system, you have the option of using a sediment filter first, followed by a carbon filter, then the third canister is available for filtering bacteria, metals, or other contaminants. You can even leave a third canister empty and use a specific cartridge when you feel the need to deal with any issue that the sediment and carbon filter won’t handle. When using multiple canisters, especially in standard size like most customers use, you really need to consider the flow. Your choice of filters are very important in determining what available flow you will have to shower in, etc. The finer the filter cartridge, the more restriction there will be. The more cartridges you use, the more the flow will be affected. So there is always a compromise to be made between the coverage and number of filters you would like to use, versus what kind of shower you can expect to take with what comes through those filters in flow. This is why we also offer jumbo size filters. They have three times the capacity in media in each cartridge and the resistance and impedance to flow is minimized. For some, this is a good option. If that is of interest, take a look in our jumbo canister section.
As far as specific filters, there are a lot of choices. The sediment filter could be either the disposable type or the wash-and-reuse. For the carbon filter, many of our customers like the modified fiber block filters we sell. They seem to give better overall performance and flow over the life of the filter, and they are naturally resistant to stagnation, which is more of a factor for part-time RVers. So, here are some recommended combinations: 5-micron sediment (RV-SED5 or PR5) & F5 carbon; 1-micron sediment (RV-SED1 or PR1) & F1; or, 1-micron sediment (RV-SED1 or PR1) & F1Pb. The choice comes down to how much “stuff” you want to remove from your water supply. The 5-micron sediment/F5 combo removes the least (although still quite good) and provides the best flow and pressure. The 1-micron sediment/F1 combo is a finer set of filters that can remove cysts (giardia and cryptosporidium), with only a minimal reduction in flow and pressure. The 1-micron sediment/F1Pb combo is similar to the previous one, but it adds the ability to remove lead and heavy metals as you mentioned. All of the systems will supply high-quality water to your RV with sufficient flow and pressure, assuming your water supply at the park is not insufficient.
To further purify your drinking water, you could add additional filters under your sinks, or you could install a drinking-water reverse osmosis (RO) system. Most of these drinking water systems are fairly slow-flow, and they wouldn’t produce enough water to run your normal sink faucet. They are usually set up with a separate dispenser faucet. The RO would provide bottled-water quality in a relatively inexpensive system, and if you buy the filters I described above for your whole RV, you could use our Custom package to save on space and cost. Most users of these systems install them under the kitchen sink and only have the purified water available there. As you can see, the possibilities are extensive. I hope this helps, and please let me know if you have more questions. Thank you for your inquiry!