A fair amount can be learned about household water with nothing but a clear glass, a bottle of soap and ten minutes, and one free document answers more than any home test. What none of it does is address safety, so it is worth being clear at the outset about which questions these methods settle and which they cannot touch.
The settling test
Fill a clear glass and let it stand for an hour on a white surface. Cloudiness that clears from the bottom upwards within a minute is dissolved air, which is harmless and common on cold mains. Particles settling and the water clearing from the top down means suspended material, typically oxidized iron or disturbed sediment. Water that stays uniformly coloured suggests something dissolved: iron not yet oxidized, manganese, or tannins. That single observation narrows the field considerably.
The soap test for hardness
Put a third of a clear bottle of cold tap water in, add a few drops of plain liquid soap without moisturisers, cap it and shake hard. Thick suds that last, with clear water below, indicates soft water. A thin scum with little lasting foam and cloudy water below indicates hard. The USGS classifies hardness as dissolved calcium and magnesium, from soft at 0 to 60 mg/L as calcium carbonate through to very hard above 180, and this test reliably separates the ends of that scale.
Read the house
The appliances have been measuring your water for years. Crust on the kettle element and the shower head is hardness, and how quickly it returns after descaling indicates how hard. Orange staining is iron; black is manganese; blue green is dissolved copper from acidic water. A rumbling water heater is scale on the element. Soap that will not lather and glassware that films are hardness. Two or three of these together is more convincing than any single sign.
The free document, and the limit of all of this
On a community supply the utility publishes an annual report giving hardness, the disinfectant used and required monitoring results, which is specific to your system and costs nothing. What none of these methods reveals is bacteria, nitrate, arsenic, lead or chemicals, all of which are invisible, tasteless and matter at concentrations no home observation can detect. For those the answer is an accredited laboratory. Our home test kit guide covers what to send and when.
Questions people ask about how to test water quality at home without a kit
Can I check hardness without a kit?
The soap shake test in a clear bottle separates soft from hard reliably: thick lasting suds means soft, thin scum means hard.
What does cloudy water that clears from the bottom mean?
Dissolved air, which is harmless and common on cold mains water. Clearing from the top down means suspended particles.
What can staining tell me?
Orange is iron, black is manganese, blue green is dissolved copper from acidic water attacking the plumbing.
What can none of this detect?
Bacteria, nitrate, arsenic, lead and chemicals, all of which are invisible and matter far below what observation can reveal.