As one who's been deeply involved in the engineering of bio-pharma, ultraclean, food grade, etc. systems involving filtration, etc. ..... you have to ask yourself the following very important question: what is it you are 'trying' to 'filter' out of the water? .... chemicals, bacteria, "rust sticks and feathers", viruses, oocysts, etc. etc . etc.??? WHAT ???????
Are you looking for 'hygienic safety', potable water that meets 'some acceptable specification' so that you can drink and wash with some surety, etc. ??????
Do you know how to change out a filter .... and not contaminate the whole system when you do?
Do you KNOW how to sanitize the system?
Do you know what levels of chlorine to add to the system to keep it hygienic and safe?
If you're not asking these specific questions you are probably wasting your $$$$.
Except for providing a false and totally unwarranted sense of security, these 'filters' are not going to do very much for your 'system'. Bacteria uses the carbon in 'carbon filters' as its nutrient source and then thrives, Carbon removes the needed chlorine that attenuates bacterial etc. growth, the hardware store filters only remove 'rust, sticks, and feathers and are too large in µM retention (and removal efficiency AT that µM 'rating') to retain even large bacteria, mold & mildew spores, viruses, etc. etc. etc. etc. Many of the 'nasties' (oocysts) that can enter your tankage from even municipal water sources are resistant to chlorination. Bacteria and other organisms that are retained on filtration media ultimately die and then breakdown .... and ultimately the cell fragments (metabolites) that go back into solution are or can be the toxins, etc. that cause fever and give 'sickness'.
The SIMPLE solution is start out with a CLEAN tank and delivery system ... not just an occasional 'shock sanitization' with chlorine/chlorox ... but a thorough 'mechanical scrubbing' with strong soap and water. Would you eat from dirty dishes or drink from cruddy glasses that were only briefly soaked in clorox? Mechanical scrubbing removes the (usual) MASSIVE bacteria colonies that are growing on the walls, etc. of the water tank and the inside of the piping (bacteria use the materials of the walls and piping as their nutrient source !!!!!!!! --- have you ever looked inside the tank on a common toilet?). You 'must' open the tank and reach in with your bare hand and feel for any 'slime' thats attached to the walls, etc. .... if so, thats a massive bacterial colony (calcyx) and it must be removed by mechanical scrubbing. Shock sanitization is ONLY valid IF and ONLY IF the system is free of bacterial 'slimes', etc.; and, or only 'proper' if the system is BRAND NEW and never used/comissioned.
After the system is CLEANED, THEN you sanitize with a heavy dose of clorox, etc. Then after filling the tank (with appropriate 'filters' attached to the charging hose prevent contamination from entering INTO the system) you add a wee bit of chlorine (clorox, etc.) to control any bacteria that did pass the charging filters, the municipal water treatment, etc. How much chlorine? add just enough chlorox so that when the water that comes out of the spiggot ---- your WIFE can 'just BARELY smell the 'faintest' odor of the chlorine'. Dont depend on 'recipies' that you find on the internet of how much chlorine to add, too much chlorine is dangerous and unhealthful, too little is dangerous and will lead to an 'unhealthy system'. (Standard municipal water system is typically in the range of 1+ parts per million chlorine.)
If you want to add a filter ..... put it on the tank VENT !!!!!!!!! Every time you draw down water, air rushes into the vent ... and air is laden with bacteria, mold and mildew spores. The tank vent line being open and in direct contact with the atmosphere, has HIGH humidity, usually in a dark place .... is a fantastic place to 'culture' bacteria, mold, mildew, etc. .
...... Put a 'hydrophobic' bacterial blocking filter on the vent and keep that filter DRY --- about $75.00 for such a 'capsule filter' from a filter manufacturer that serves the bio-pharm, etc. industries. OR take a fist size wad of bandage cotton, apply over the end of the vent, cover with a bit of bandage gauze to keep the cotton in place, keep dry and change yearly.... about $0.25 (BTW --- when you inspect the total length of the vent line, you will probably projectile vomit when you realize what is growing inside it ... a filter on the vent will prevent this. If the vent line isnt sparkling clear/clean - replace it.)
Any of the 'clear plastic' in the water system that has turned 'dark' or discolored should be replaced .... it means possibly that funguses, mildews, etc. have penetrated INTO the plastic and or the plastic is breaking down and the fragments are 'leaching' into the water.
Keep the tank EMPTY when not using the boat ..... stagnant water is a fantastic breeding ground for bacteria, etc. You dont keep your portable 'water cooler' always filled do you? ... and you know why too: old water gets 'funky' when bacteria start to grow in it.
If your water 'smells' .... Clean the tank, remove any 'fiberglass' from the system or any 'plastic' that in not rated 'food grade'; shock sanitize after cleaning .....
filter the water as you FILL the tank, using 2 filter: 1. that is ***FDA RATED/CERTIFIED to remove 99.9% of 'cysts' or 'oocysts'***. 2. a carbon filter. These are attached to the hose with which you fill the tank.
If you use a carbon filter in the 'fill set', run the water AS SLOW AS POSSIBLE ... as it takes 'contact time' in the carbon filter to adsorb the 'undesireables' .... the slower the fill the better adsorption to the carbon
If you properly filter the water BEFORE it gets to the tank when filling, maintain a clean and hygienic system, ...... then remove ALL filters from the boat as they 'trap' bacteria on their filter media (the filter media will 'concentrate' the bacteria)... and when these bacteria ultimately build up into a thick 'slime' and then die, they then release all their toxins and metabolites' into the water. If after all the above, the water still smells funky ... then add a carbon packed filter ON the spigot outlet.
REmove any tank that is 'fiberglass' made from any form of 'styrene', or any epoxy that is not certified for use in 'potable water'.
BTW - water filters are or should be installed on the PRESSURE SIDE of any pumping system.
Filter (particles, cysts, etc.) BEFORE they get into the tank. Maintain regularly the tank hygiene, CLEAN it when necessary. Put a filter on the tank VENT and keep it DRY. Never substitute 'sanitization' for mechanical scrubbing, but do sanitize after mechanical scrubbing. Keep enough chlorine in the water ... just enough so that your WIFE can detect the 'barest smell' of the chlorine in the spigot water. Empty the tank when the boat is not being used.
SIMPLE stuff that will result in 'non-funky' water and water that is reasonably safe to wash and drink