El agua de San Diego es dura, y sus electrodomésticos llevan la cuenta

San Diego County grows very little of its own water. Most of what comes out of the tap has been imported — down the Colorado River Aqueduct or the State Water Project — and river water that has spent a few hundred miles in contact with rock arrives carrying a lot of dissolved calcium and magnesium. That is what "hard" water means. It is not a contaminant and it is not a health problem. It is simply mineral that is in the water on the way in and not in the water on the way out, because it stays behind in your machines.

Every appliance that heats water is, whether it was sold to you this way or not, a device for separating mineral from water. Heat drives the calcium out of solution and it plates onto the hottest surface available. In a dishwasher that is the heating element. In an ice maker it is the mould and the fill tube. In a washing machine it is the inlet valve screens and the heater, if it has one.

Find your own number before you do anything

Hardness is not one figure for the whole county. It varies by the agency that serves you and by what mix of imported and local supply they are running that year, and the difference between neighbouring cities can be real. Do not take a number off a blog — including this one.

Every water supplier in the United States is required to publish an annual Consumer Confidence Report, and hardness is on it. Search for your city or water district plus "water quality report" and you will have the current figure in about a minute. It will be given either in parts per million or in grains per gallon; divide ppm by 17.1 to convert. Roughly speaking, under 3 grains is soft, 7 to 10 is hard, and above 10 is very hard. Much of this county reads in the upper half of that scale.

Knowing the number matters because it decides whether a softener is an investment or an expensive way to feel proactive. At the top of the range it changes the life of a dishwasher. At the bottom, rinse aid and a descaling habit do nearly as much for a hundredth of the cost.

What it actually does, appliance by appliance

In a dishwasher, hard water shows up first as cosmetics and later as a fault. The cosmetic stage is a white haze on glassware and a chalky film inside the tub. What is happening underneath is that scale is building on the heating element, which then has to run longer and hotter to reach the same temperature. Elements fail early on hard water, and the spray arm holes narrow until the top rack stops getting clean.

In an ice maker, scale is the single most common reason a unit that used to make good ice starts making cloudy, small, or hollow cubes. The mould loses its release, the fill tube narrows, and the cubes come out misshapen or stick together in the bin. This one is worth catching early, because a neglected commercial machine can go from a descale to an evaporator replacement.

In a washing machine, the effect is quieter. Mineral collects on the inlet valve screens and reduces fill rate, which reads as "it takes forever to fill" long before it reads as a fault. Hard water also makes detergent work less well, which is why people in hard-water areas tend to use more of it — and excess detergent is itself a cause of residue and odour complaints.

Three things worth doing

• Use rinse aid in the dishwasher, and keep the dispenser filled. It is not a luxury additive in a hard-water county — it is what stops the mineral drying onto the glass. This is the highest-return thing on the list and it costs a few dollars a month.
• Descale on a schedule rather than when you notice. Citric acid dishwasher cleaner, run on the hottest cycle with the machine empty, two or three times a year. For an ice maker, use the descaler the manufacturer specifies — the acid concentration is chosen for the materials in the water path, and vinegar is not a substitute in a machine with aluminium in it.
• Change the refrigerator water filter on time. A filter does not soften water, but a spent filter restricts flow, and restricted flow to an ice maker produces exactly the small hollow cubes people assume mean a dead unit.

A whole-house softener is the real fix and it is a real expense — equipment, installation, salt, and in some places a restriction on discharging the regeneration brine. If your report puts you at the hard end, get a quote and do the arithmetic against what you spend on appliances. If you are in the middle, the three habits above capture most of the benefit.

When it has already gone past housekeeping

Descaling solves a scaled machine. It does not solve a failed heating element, a valve that no longer closes, or an ice maker whose mould heater has burnt out — and running acid through a machine with one of those problems just wastes an afternoon. The line is roughly this: if a cleaning cycle makes a visible difference, keep cleaning. If two cleaning cycles change nothing, the part has already failed and it needs a diagnosis.