Even if you're a novice do-it-yourselfer, you'll be able to fix leaky and slow-flowing faucets if you properly prepare for the task.
First, identify your faucet's manufacturer (the brand might be stamped on the faucet) and determine if the faucet is washerless and operates via ceramic disk, a cartridge, or ball valve. Old two-handled stem faucets have compression systems equipped with washers that open and close as handles are turned. Repair techniques and tools vary by faucet type, but there are general rules and supply lists that apply to most kitchen sink faucets.
Before you fix a leak, note the location of the leak or leaks to help you choose the correct solution. Is the kitchen faucet leaking from its neck? Is it seeping from the spout's base or at the handle? Or is your kitchen faucet leaking under the sink?
Once you've identified the leak's location, turn the shutoff valves beneath the sink and place a rag in the sink's drain so tiny parts won't be lost. As you disassemble the faucet, take notes or digital images of the process and parts' placements to ensure you correctly reassemble the faucet. Set aside worn parts to take them with you to the hardware store. Wipe valves clean. Soak mineral-crusted parts in vinegar.
Learning how to fix a kitchen faucet requires a small collection of tools and materials. Shop for kitchen faucet repair kits designed for your type of faucet. They generally include O rings, a small tool or two, and style-specific replacement parts such as a ball valve, stems and washers, or a cartridge. Pick up a tube of plumber's silicone grease to make slipping on new seals easy. You might also want to buy a universal O-ring kit so you have a range of seals to draw from. Other tools you might need include a small Allen wrench set, screwdrivers, slip-joint pliers, needle-nose pliers, and a utility knife.
Leaky faucet repairs fall into four categories with slightly different fixes for each:
Water-flow problems. Mineral deposits or other gunk might build up and block water flow. Use a screwdriver to gently chip away debris; turn water back on to flush out the dirt. Reassemble the faucet, and turn on water to check flow. Still sluggish? Remove the aerator at the spout's end; soak in vinegar; and clean with a toothbrush.
Drips at the spout's end. For a ball valve faucet, replace the seats and springs, tighten the adjusting ring, and replace worn O rings. If it's a cartridge-style faucet, remove the cartridge and replace the O rings on the cartridge. Ceramic disk faucets rarely leak, but if they do, replace cartridge seals and O rings. For compression/stem faucets, replace washers; if leaking persists replace the seat and the stem.
Leaky handles. For single-handle washerless faucets, remove the handle and gently tighten the cap/adjusting ring to which the handle connects. For compression faucets, remove handles and replace O rings.
Leaks at the spout's base. For a kitchen faucet leaking at the base, remove the spout, replace all O rings, and clean valves.
If you can't fix your faucet, it's time for a replacement. Choose a faucet compatible with your sink's existing cutouts to make installation easy. Check how many holes are in your sink by looking at the sink from below; standard faucets require one to three holes. Depending on the number of holes, you might be able to install a sprayer, soap dispenser, or other components. If you want a more extensive upgrade, replace the sink, too, and buy a new model that has the number of cutouts needed to accommodate your preferred faucet and configuration of add-ons.