You can usually tell hard water from three everyday signs: white crust on faucets and kettles, soap that will not lather properly, and spots left on glassware after it dries. Confirming it takes a test, because the actual number decides whether you need to do anything and, if you do, what size of softener the household needs.
What hardness actually is
The USGS defines hardness as dissolved calcium and magnesium, expressed as calcium carbonate, and classifies water as soft from 0 to 60 mg/L, moderately hard from 61 to 120, hard from 121 to 180 and very hard above 180 mg/L. Those minerals come from the rock the water moved through, which is why hardness is a regional property: limestone country gives hard water, granite and sandy country generally gives soft. Nothing about hardness is a health problem. What it does is form scale when water is heated or evaporates, and react with soap instead of letting it lather.
The signs around the house
Look at the aerator on your kitchen faucet and the element or base of your kettle: chalky white deposit there is scale. Check the shower door and tiles for a film that returns quickly after cleaning, and glassware for cloudy spots that are still there when dry. Soap and shampoo that take a lot of work to lather, and a filmy rather than squeaky feel on skin, both point the same way, as does laundry that comes out stiff or dull. A water heater that is noisier than it used to be, or a dishwasher that leaves residue on everything, are later stage symptoms of the same thing.
Testing it yourself
A soap shake test is the crude version: half fill a clear bottle with water, add a few drops of pure liquid soap, cap it and shake. Soft water throws up a generous head of suds that lasts; hard water gives thin, quickly collapsing bubbles and a cloudy liquid underneath. For a number rather than an impression, use a hardness test strip or a titration drop kit, both sold cheaply and both accurate enough to size equipment. Test the cold tap, and on a well test it seasonally, since hardness moves with the water table.
Getting the number confirmed
If you are on a public supply, your utility publishes an annual Consumer Confidence Report and the EPA maintains a finder for it. That report gives the hardness of the water delivered to your area, which is enough to plan with. Well owners need their own laboratory test, and it is worth running hardness alongside iron, manganese and pH, since those three change which equipment is appropriate. Bring the number to any vendor before discussing systems, because softener sizing is a calculation from hardness and household use. Our guide to the best shower head for hard water covers the cheaper fixes if you decide against a softener.
Questions people ask about how do i know if i have hard water
Is hard water bad for you?
No. Hardness is dissolved calcium and magnesium and is not a health concern. The problems it causes are scale in appliances and pipework, poor lathering and spotting.
What counts as hard water?
The USGS classes water as soft from 0 to 60 mg/L as calcium carbonate, moderately hard from 61 to 120, hard from 121 to 180 and very hard above 180 mg/L.
Can I tell hard water just by looking?
The signs are strong indicators: scale on faucets and kettles, spotted glassware and poor lather. Sizing a softener still needs an actual measurement.
Does hard water change with the seasons?
On a well it can, because the water table moves and the water contacts different rock. Retesting seasonally is worthwhile before committing to equipment.