Most under sink water filter problems can be easily resolved without calling a professional plumber. Common issues include clogged filters, tank damage, and water type. To assess the problem, get an old towel to catch any drips and a flashlight, because areas under sinks are usually fairly dark.
Problem 1: Clogged Filter
When is the last time the filter was changed? The job of a filter is to trap particles in water to keep them from coming out the tap. Most water filtration system manufacturers recommend changing the filter screen out at specific regular intervals, such as monthly or every 90 days. If the filter has done its job for too long, it may simply be clogged up with gunk. This is an easy fix: replace the filter. If the filter is reusable, then clean it thoroughly, put it back, and it should be good to go.
Once the filter has been replaced, run water through it to make sure the system is now working as it should. If there still seems to be a problem, there may be a component within the filter pump that has gone bad or simply needs cleaned. If you can easily take the system apart, check for gunk build-up inside that might be restricting water flow. If there is no corrosion or clogging, the pump may be bad. Sometimes they just wear out, and working hard against a clogged filter for too long will wear them out more quickly.
Problem 2: Tank Damage
Most water filters require the water to be moving through it at a good clip in order for the filtration system to work properly. The water tank may have hit the end of its life span, or may be overly corroded and simply cannot deliver the water to the filter at a high enough pressure, and may need to be replaced. There may also be a problem with the pressure the tank is receiving. Check the pressure of the tank and make sure it is set correctly for the area's municipal water pressure. This pressure can vary from block to block in a neighborhood, and may make a difference in the functioning of your unit. If the pressure to the dwelling is low, this may be a larger problem with clogged pipes from the street, such as debris build-up or tree roots.
Problem 3: Water Type
Sometimes water in the area is just too difficult for a filter to manage and work correctly. This could be caused by extreme hard or soft water, which often causes mineral sediment build-up in pipes and filters quite quickly. In this case, a water purifier system might be the answer. Water purifiers tend to have a longer life span than water filters. Some purifiers are filter free, and others still have a filtering system within it, and so a filter may still have to be changed regularly, but the unit itself may be more reliable in the long run.