--- title: "Hard Water and the Coffee Machine Filter: Test Strip, Hardness Level, Cartridge" description: "How to read the strip in the box, convert a utility's milligrams per liter to the machine's scale, when a filter cartridge earns its place and which water never…" url: "https://coffeemachinerepair.center/guides/hard-water-and-the-filter/" date_modified: "2026-09-26" --- Installation and setup # Hard Water and the Coffee Machine Filter: Test Strip, Hardness Level, Cartridge Coffee machine water hardness is set once, at first use, from the test strip in the box or your water utility's figure. The machine uses it to decide when to ask for descaling. A water filter cartridge lowers scale and is changed when the display asks or at the maker's interval. Mineral water, softened or reverse-osmosis water can harm some machines. By [CoffeeMachineRepair.center technical team](https://coffeemachinerepair.center/authors/technical-team/) Published September 26, 2026 ## At a glance. Out of the box, most fully automatic machines assume water of a certain hardness and count drinks toward the next descaling on that guess. Set the right value on day one, decide about the filter, and the machine asks for descaling when it actually needs it rather than months too late. Read the whole guide ### How to measure The test strip from the box Dip it about one second and read it after about a minute. ### Factory setting Often hard or very hard Miele ships at level 3 of 4, Bosch at level 4 of 4. ### Filter change When the display asks, or by two months Bosch's limit for its cartridge. ### Not in the tank Mineral water or reverse-osmosis water Miele warns both can damage its machines. In this guide 1. What water hardness does inside a coffee machine 2. Measuring your water before the first cup 3. Setting the level on the machine 4. The filter cartridge: when to use it and how to change it 5. Water to keep out of the tank 6. Step by step 7. Questions ## What water hardness does inside a coffee machine The minerals that make water hard are mostly calcium and magnesium in solution. Every time the machine heats water, some of it stays behind as scale on the heater, in the valves and in the narrow tubes. Miele explains its hardness setting in exactly those terms: the harder the water, the more often the machine needs descaling. The machine cannot see scale. It counts water and steam, multiplies by the coffee machine water hardness you entered, and asks for descaling when the total reaches its limit. Enter a value that is too soft and the request arrives late, after scale has already narrowed the paths; enter one that is too hard and you descale more often than you need to. ### What scale looks like from the outside You will rarely see it directly. The signs are slower drinks, coffee that is not as hot as it was, a pump that sounds strained and a white crust around the water tank valve. By the time these show, a descaling cycle is overdue. Source: [Miele — CVA 6405 built-in coffee system, operating and installation instructions](https://us.mieleusa.com/mielemedia/docs/products/opin/coffee%20machines/cva6405_coffee%20system%20manual.pdf) — Harder water means more frequent descaling; the machine counts water and steam used; test strip dipped about one second, read after about a minute; the water authority can give the hardness; four levels in gr/gal, factory level 3; no mineral or reverse-osmosis water; change the water daily ## Measuring your water before the first cup Almost every maker packs a test strip in the box. Miele's instructions are typical: dip the strip in drinking water for about a second, shake it off and read the result after about a minute. JURA asks for the strip to be held under running water for a second, and counts the fields that turn red. If the strip is lost, the local water utility can give you the figure; Miele suggests asking them. Utilities often quote hardness in milligrams per liter as calcium carbonate, while the machine's menu may use grains per gallon or German degrees, so convert before you choose a level. One grain per gallon is about 17.1 milligrams per liter. *USGS hardness classes, with the same limits in grains per gallon* | USGS class | mg/L as calcium carbonate | About grains per gallon | | --- | --- | --- | | Soft | 0 to 60 | 0 to 3.5 | | Moderately hard | 61 to 120 | 3.6 to 7.0 | | Hard | 121 to 180 | 7.1 to 10.5 | | Very hard | More than 180 | More than 10.5 | ### Homes on a private well There is no utility report for a well, so the strip is the only quick answer. USGS notes that hardness is a particular concern with groundwater, which is why a house on a well should test again after any change to its treatment equipment. Source: [USGS — Hardness of Water](https://www.usgs.gov/special-topics/water-science-school/science/hardness-water) — 0 to 60 mg/L as calcium carbonate is soft, 61 to 120 moderately hard, 121 to 180 hard, more than 180 very hard; groundwater systems are concerned with hardness; [Miele — CVA 6405 built-in coffee system, operating and installation instructions](https://us.mieleusa.com/mielemedia/docs/products/opin/coffee%20machines/cva6405_coffee%20system%20manual.pdf) — Harder water means more frequent descaling; the machine counts water and steam used; test strip dipped about one second, read after about a minute; the water authority can give the hardness; four levels in gr/gal, factory level 3; no mineral or reverse-osmosis water; change the water daily; [JURA — E8 instructions for use](https://us.jura.com/-/media/global/pdf/manuals-na/Home/E8/download_manual_e8_e80_ul.pdf) — Hold the Aquadur strip under running water one second, read after about a minute; filter cartridge recommended at 10 °dH or more; sparkling mineral water and other liquids can damage the tank; fill with cold water only, never warm or hot Close on a water filter cartridge being screwed into the tank of a coffee machine. ## Setting the level on the machine Makers use different scales, so read the numbers in your own manual rather than matching level names. Miele offers four levels in grains per gallon: soft up to 8.7, medium to 14.6, hard to 21.9 and very hard above that, with level 3 set at the factory. Bosch's built-in also has four levels, starts at level 4, and asks owners with a household water softener to choose level 3 or its softening-device setting. Enter the value during first setup if the machine offers it, or later under settings. If you move house, install a softener or switch from a well to city water, change the setting the same day. - Read the strip or the utility figure and note the unit it uses. - Convert it to the unit your machine's menu shows. - Pick the level whose band contains your number, not the nearest name. - Recheck after any change to the house water. Source: [Miele — CVA 6405 built-in coffee system, operating and installation instructions](https://us.mieleusa.com/mielemedia/docs/products/opin/coffee%20machines/cva6405_coffee%20system%20manual.pdf) — Harder water means more frequent descaling; the machine counts water and steam used; test strip dipped about one second, read after about a minute; the water authority can give the hardness; four levels in gr/gal, factory level 3; no mineral or reverse-osmosis water; change the water daily; [Bosch — BCM8450UC built-in coffee machine, use and care manual](https://media3.bosch-home.com/Documents/8001075609_A.pdf) — Preset hardness level 4; level 3 or the softening-device setting with a house softener; filter lowers limescale and improves taste; rinse a new filter with a 17 oz container; replace at the message or after two months at the latest; rinse after a long absence; no chemically softened water ## The filter cartridge: when to use it and how to change it A cartridge in the tank takes out part of the hardness before the water reaches the heater, and it also improves taste. Bosch describes its filter as lowering limescale, reducing impurities and improving the coffee. JURA recommends its cartridge wherever the water is 10 German degrees or harder, which is about 10.5 grains per gallon. The cartridge works only if the machine knows it is there. On most makes you tell the menu that a filter is inserted, replaced or removed, and a new cartridge must be rinsed before the first drink. Bosch has you place a 17-ounce container under the outlet for that rinse. - Register the cartridge in the menu as inserted or replaced. - Rinse a new cartridge through before the first drink. - Change it when the display asks, or at the maker's time limit. - Choose remove in the menu if you stop using one. ### How long a cartridge lasts Bosch treats its filter as spent when the replace message appears, or after two months at the latest, and says it must be changed for sanitation as well as scale. A cartridge left in past its date can hold stale water and stops protecting the heater, so an expired cartridge gives protection only on paper. ### After the machine has stood unused Water sitting in a cartridge for a week or more is not fresh. Bosch asks for the filter to be rinsed after a long break, such as a vacation, by dispensing a cup of hot water before the first coffee. Source: [Bosch — BCM8450UC built-in coffee machine, use and care manual](https://media3.bosch-home.com/Documents/8001075609_A.pdf) — Preset hardness level 4; level 3 or the softening-device setting with a house softener; filter lowers limescale and improves taste; rinse a new filter with a 17 oz container; replace at the message or after two months at the latest; rinse after a long absence; no chemically softened water; [JURA — E8 instructions for use](https://us.jura.com/-/media/global/pdf/manuals-na/Home/E8/download_manual_e8_e80_ul.pdf) — Hold the Aquadur strip under running water one second, read after about a minute; filter cartridge recommended at 10 °dH or more; sparkling mineral water and other liquids can damage the tank; fill with cold water only, never warm or hot ## Water to keep out of the tank The right water is fresh, cold tap water. Miele warns against mineral water, which leaves heavy scale, and against water from a reverse-osmosis unit, which it says will damage the machine. Bosch cautions against chemically softened water in its safety section, and JURA warns that sparkling mineral water and other liquids can damage its tank. Warm or hot water from the tap is also ruled out by several makers, and the tank should be emptied and refilled every day, even on a plumbed machine that fills itself. Source: [Miele — CVA 6405 built-in coffee system, operating and installation instructions](https://us.mieleusa.com/mielemedia/docs/products/opin/coffee%20machines/cva6405_coffee%20system%20manual.pdf) — Harder water means more frequent descaling; the machine counts water and steam used; test strip dipped about one second, read after about a minute; the water authority can give the hardness; four levels in gr/gal, factory level 3; no mineral or reverse-osmosis water; change the water daily; [Bosch — BCM8450UC built-in coffee machine, use and care manual](https://media3.bosch-home.com/Documents/8001075609_A.pdf) — Preset hardness level 4; level 3 or the softening-device setting with a house softener; filter lowers limescale and improves taste; rinse a new filter with a 17 oz container; replace at the message or after two months at the latest; rinse after a long absence; no chemically softened water; [JURA — E8 instructions for use](https://us.jura.com/-/media/global/pdf/manuals-na/Home/E8/download_manual_e8_e80_ul.pdf) — Hold the Aquadur strip under running water one second, read after about a minute; filter cartridge recommended at 10 °dH or more; sparkling mineral water and other liquids can damage the tank; fill with cold water only, never warm or hot ## Where to stop Book a visit if descaling reminders keep coming far more often than your hardness setting explains, if the machine will not accept a new filter after it has been inserted and rinsed as described, or if water runs slowly or not at all after descaling. Do not open the housing to look at the heater, and on a plumbed machine do not undo the supply connection behind a built-in to fit an inline filter yourself. Written by [CoffeeMachineRepair.center technical team](https://coffeemachinerepair.center/authors/technical-team/). Our coffee machine technicians write these guides from home visits and the service papers each maker publishes. Sources: [USGS — Hardness of Water](https://www.usgs.gov/special-topics/water-science-school/science/hardness-water) · [Miele — CVA 6405 built-in coffee system, operating and installation instructions](https://us.mieleusa.com/mielemedia/docs/products/opin/coffee%20machines/cva6405_coffee%20system%20manual.pdf) · [Bosch — BCM8450UC built-in coffee machine, use and care manual](https://media3.bosch-home.com/Documents/8001075609_A.pdf) · [JURA — E8 instructions for use](https://us.jura.com/-/media/global/pdf/manuals-na/Home/E8/download_manual_e8_e80_ul.pdf) ## Step by step. Four steps, in the order worth doing them. 01 ### Test the water Dip the strip from the box for about a second and read it after a minute, or ask your water utility. 02 ### Convert and set Convert to your machine's unit and choose the level whose band contains the number. 03 ### Fit the filter if advised Insert the cartridge, tell the menu, and rinse it as the manual shows. 04 ### Mark the date Note when the cartridge went in and change it at the message or the maker's time limit. For the heart of your home. ## Questions owners ask. ### What happens if I never set the water hardness on my coffee machine? It keeps the factory value. In soft-water areas that means descaling more often than needed; in very hard water the request can come too late. ### Do I still need to descale if I use a water filter? Yes. A cartridge removes part of the hardness, not all of it, so scale still forms and the machine still asks for descaling, usually less often than it would without one. ### Can I use bottled water instead of tap water? Plain still water is fine in many machines, but mineral water leaves heavy scale and reverse-osmosis water is ruled out by some makers. Check your manual first. ### My house has a water softener. What setting do I choose? Test the softened water with the strip and set that value. Bosch asks for its softening-device setting or level 3 in a softened home. ## The problems behind it. Each has a page of its own: what it usually means and the causes in the order worth checking. [All 17 problems](https://coffeemachinerepair.center/problems/) Problem ### Coffee Machine Descale Message Will Not Go Away 6 causes, cheapest first Problem ### Coffee From the Coffee Machine Not Hot Enough 6 causes, cheapest first Problem ### Coffee Machine Making Weak or Watery Coffee 6 causes, cheapest first Problem ### Loud Pump or Buzzing Noise From the Coffee Machine 6 causes, cheapest first ## When it needs a technician. The repairs on the right are where this guide ends when the checks do not settle it. ### Coffee machine descaling service A thorough descale of the water path and heater, a fresh filter, hardness set to match your water, and a message that clears. ### Coffee machine heater repair Diagnosing and replacing the thermoblock or boiler that heats water for coffee and steam, with its sensor and thermal cutout. ### Coffee machine pump repair Testing and replacing the pump that drives water through the coffee, with the flowmeter that counts each cup and the valves beside it. ## More in installation and setup. Setting the water hardness and the filter for your water, connecting a plumbed coffee system to the supply, and fitting a built-in so its cabinet, rails, ventilation and power are right the first time. [The whole section](https://coffeemachinerepair.center/guides/installation-and-setup/) Water, cabinet, power and filter ### Connecting a Plumbed Coffee System: Cold Line, Shutoff Valve and Pressure What the plumber runs to a plumbed built-in, why the line must be cold and flowing, where the shutoff valve should sit so you can reach it, and how to spot a slow seep in the first week. Water, cabinet, power and filter ### Fitting a Built-In Coffee System: Cutout, Airflow, Outlet and Height The cabinet decisions made before delivery: cutout and shelf, air in low and out high, a grounded 15-amp outlet within reach, a comfortable height, and what the installer does on the day. Guides ### All 18 guides Six sections, by what you are trying to find out. --- **[Read on the site: Hard Water and the Coffee Machine Filter: Test Strip, Hardness Level, Cartridge](https://coffeemachinerepair.center/guides/hard-water-and-the-filter/)** **[Book a visit with CoffeeMachineRepair.center](https://coffeemachinerepair.center/schedule/)**