Water filters will be of most concern to RVers, but even tent campers might benefit from portable water filters to free the water they are getting from campground faucets from sediment etc. Whether the campground is on a well or a public water system it might contain stuff you'd rather not ingest. One way to protect yourself and your family is to filter ALL the water you use. Pretty much any filter will remove sediment and really good filters will also remove chemicals and bacteria. Most of the time you can trust water from campgrounds, but sometimes I've found it to be over-chlorinated or otherwise unpleasant to drink. Unless you have verified the safety of water in lakes and streams, always assume it it is contaminated and purify it before drinking, washing wounds, or using it for cooking.
Water filters may be just as useful on boats. Many boats, especially those used for cruising, have on board fresh water sources. Using filters to fill holding tanks or purify water as it it used is as important on boats as it is in RVs Some boats used on salt water have water collection systems that either collect rain water or make fresh water from salt water. In either case a filter might help ensure the quality of water for drinking. You should always filter water when filling holding tanks to avoid introducing contaminants that could pollute your fresh water supply.
Water filters will help keep your fresh water fresh. You can use an in-line filter connected between the faucet and your hose when you fill your tank or connect to city water or you might install an internal filter to clean water as it is used. Filling your fresh water tank with filtered water helps prevent buildup of silt and other contaminants in your fresh water tank. Some filters even help remove bacteria as well as sediment. For camping and hiking you might choose a portable water filter. Filters will remove sediment and some types of bacteria but usually won't remove chemical contaminants or all microbes. Filtering out sediment will help keep your water clean and tasting pleasant.
Portable in-line filters are individually inexpensive but having to replace them fairly often drives up the overall cost. They are also very convenient to use. They require no permanent installation. You simply screw them onto the faucet, then screw your hose onto the filter and fill your tank or connect to your city water inlet. You could install the filter on the other end of your hose, but it gets in the way of putting the hose into the gravity fill spout on your RV and tends to stress the city water inlet and kink the hose on the side of your RV. If you fill your RV through the city water hookup the filter would stick out and you may risk breaking the plastic mounting plate for the connection. In-line filters are fairly small (about the same size as the cartridge for a grease gun) and therefore get clogged or used up rather quickly and have to be replaced, but is is an easy way to remove sediment from your water when filling your tanks and jugs or connectiing to city water with no difficult installation procedures. It is often a small price to pay for convenience. When using an in line filter with your city water connection, still use a pressure regulator between the faucet and the filter. As the filter begins to clog up you might want to move the pressure regulator to between the filter and the hose. You always want the pressure regulator where it will protect your hose as well as your RV plumbing.
Whole system or internal filters will cost more initially and require some installation, but the filter elements usually last longer than in-line filters so you don't have to replace them as often and are usually less expensive to replace in the long run. And they are more convenient. Once installed you only need to check and replace the filter now and then. You can buy filter systems designed for RVs at RV supply stores but you can probably get suitable models for less at a home improvement store that can be adapted for RV use. You may have to purchase extra fittings to attach them to the water lines in your RV. RV plumbing usually is different from residential plumbing and may require special tools or connections. If you have any worries about doing the installation, take it to a qualified RV technician. You will need to find a location where there is enough room for the filter, access to the water lines, and convenient access to replace the filter element. You want to install the filter where water from both the city water connection and the 12-volt pump will pass through it before being distributed to the fixtures in your RV. Make sure it filters water that goes to the water heater too. Consider the location when you purchase the filter. Some filters can be opened from the top to replace the element. Some have canisters that need to be unscrewed from the bottom. Make sure the one you buy will be convenient for you to service. If you have a permanently installed water filter and live in an area where you get freezing winter weather, be sure to winterize your filter along with the rest of your system. Depending on your personal taste and budget there are many different filter options, including fancy "reverse osmosis" filters, but standard filters, especially those with charcoal components, are usually adequate. Typically, the more you are able or willing to spend, the cleaner your water will be. However a basic filter will screen out most particulates and is usually adequate to provide acceptable water without the expense of fancy reverse osmosis filter systems.
You can adapt large, residential style filters for use as in-line filters to be used to either fill your fresh water tank or connect to your city water inlet. You need plumbing fittings to adapt the inlet and outlet of the filter (usually 1/2" pipe fittings) to hose fittings. This gives you the extra capacity and usually lower cost of the larger filters without the hassle of making a permanent installation. You will need a short piece of potable water hose in addition to your usual hose in order to connect the filter in line. Make sure the filter doesn't hang of the side of the RV or off the faucet. It needs to sit on the ground to avoid damage to the hose or connections. You may want to make some sort of cage or box to contain the filter and keep it from getting kicked or tipped over. Always place the filter next to the campground pedestal or under your RV so it doesn't become a trip hazard.
And remember to always use hoses rated for potable water. Ordinary garden hoses might do in a pinch, but they can leech plastic taste into your water -- especially when used as a city water hookup where the water may sit in the hose for long periods of time and may be exposed to sunlight.
Portable water filters are generally designed to provide clean drinking water for one person. Typical design looks like a water bottle. They usually have replaceable filters so they can be reused. Each filter typically handles up to 300 gallons of filtration. Personal water filters also come in the form of straws you can use to drink directly from a container or a stream.
For tent camping and hiking you can get personal water filters. Sometimes these consist of a water bottle with a built in filter at a reasonable. I think I paid about $20-25 for mine. There are even some very compact "drinking straw" filters which are especially convenient when backpacking. These personal filters let you purify drinking water from just about any source.
For more information about RV water filters see http://www.rvwaterfilterstore.com/. They offer a variety of filter systems specifically designed for RVs.
With proper filtration you can be sure of fresh, clean water wherever you go.
Drink up!