Black particles can come from 2 common sources: a broken water filter, a degrading faucet washer or gasket, or a disintegrating black rubber flexible supply line hose (for a water heater, washing machine, or kitchen faucet, etc.).
If the particles are very hard, similar in size and shape, and look like large coffee grounds, they are probably granular activated carbon (GAC) particles from the inside of a GAC water filter that you have installed. Replace the filter cartridge or consult with the manufacturer or the vendor who sold it to you.
If the particles are solid but rubbery in texture, they could be pieces of an old disintegrating faucet washer or gasket. If this is the problem, the particles would likely only be present at one faucet and that faucet may be leaking. Replace the faucet washers and the packing at the ends of the supply lines.
If the particles are small black particles that can be easily smeared between two fingers, they are probably from the inside of a flexible hose. These black rubber hoses are covered with a braided stainless steel mesh. Over time, the chlorine in the water causes the rubber to break down. Replace the hose, ideally with a liner that is identified as chemical or chlorine resistant. Black rubber hoses typically have a one-year warranty while the more chemical resistant hoses have a 5-year warranty.
Brown or orange particles are typically rust particles that have broken off the inside of your water pipes or the SUB water mains. These particles are very hard, irregular in size and shape, and can be several different colors (including black). They consist of mostly iron and are not a health hazard but they are a nuisance if they clog washing machine screens, showerheads, or faucet aerators.
Another common cause of brown or orange particles in the water is a broken water softener. A water softener contains many small, round beads (or resin) for softening water. The beads will be uniform in size, typically the size of fish eggs, and are brown or orange. The mechanism that keeps these beads in the tank can break, releasing them into your water. Call your service agent for repairs.
Aerators are strainers attached to your faucet or showerhead that break up the flow of water as it leaves your tap. Aerator screens can collect particles found in water and should be routinely cleaned throughout the year and replaced once a year. Particle buildup is often white and comes from a variety of sources.
The most common source of buildup in aerators is from the hot water heater. The hot water heater dip tube is made of a nontoxic plastic material called polypropylene. This plastic can break apart or disintegrate and travel in the hot water to your faucet, eventually collecting in the aerator.
If you leave filter jugs, vases and pet water bowls in sunlight, algae will start growing. You can prevent algae growth by changing the water and cleaning the water jug, vase and bowl regularly. Always keep your filter jug in the fridge, away from heat and light that can encourage the algae to grow.