Before you price a whole-house filter or a softener, spend a week finding out where the problem lives. A complaint about water that is cloudy, smells, tastes off or leaves marks can come from the source water that enters your house, from the pipes and fittings inside it, or from the water heater. Each one needs a different fix, and the cheapest way to avoid paying for the wrong one is to map where and when the symptom appears.
Start with which taps show it
Walk the house and test every tap that gets water, one at a time, with the same procedure: run the cold tap for a minute, then note the appearance, smell and taste. Then do the same for the hot tap. Write down the results on the same sheet every time so you can compare them later.
If the problem appears at every cold tap and the hot tap too, it is probably coming in with the supply, which means the source or the service line is the first suspect. If it appears only at one tap, look at what is attached to that tap and what it connects to, such as a refrigerator line, an ice maker or a faucet with an aerator that has collected debris. A single-tap problem rarely justifies whole-house equipment.
Check whether it is hot only
A symptom that appears only on the hot side is a strong signal that the water heater is involved. Sediment settles at the bottom of a tank over time and can change how the water looks, and some tanks contain a sacrificial anode rod that can react with the water and produce a sulfur or rotten-egg smell in the hot line only. The cold line runs clean in that case, and that difference is the key clue.
Before you blame the heater, confirm the cold line is clean at the same tap. If it is, have a plumber or the heater's service provider look at the tank, its drain valve and the anode, since those are the parts that decide hot-only problems. Water treatment equipment on the cold line will not fix a problem created inside the tank.
Check the timing
When the symptom shows up matters as much as where. Note whether it appears only on the first draw in the morning, only after the house has sat empty for several days, only after street work or main repairs in your area, or only after a heavy rain. Water that sits in pipes for a long time can pick up flavor and color from the pipe itself, and a sudden change after outside work points toward the supply rather than your plumbing.
Timing also helps you decide what to ask a provider or a utility. A problem that appears on a schedule is far easier to describe, and easier to trace, than one that comes and goes at random.
Write it down and decide the next step
Keep a simple log for two or three weeks: the date, the tap, hot or cold, what you saw, smelled or tasted, and whether the water had been sitting. A clear log turns a vague complaint into something a plumber, a utility or a testing lab can act on. If the cold supply is affected at several taps and the log shows it is persistent, a water test by a certified lab is the next step, and that test should guide any equipment choice. Our methodology page explains how we judge providers when they recommend equipment based on a test, which is a useful thing to check before you accept a recommendation.
If the problem is limited to one tap or to the hot side, you may not need treatment at all. Solving the wrong problem is the most expensive outcome, and the map you have just made is what prevents it.