Water hardness in Duque de Caxias
9 mg/L soft
Tap water in Duque de Caxias is soft: 9 mg/L (0.5 gpg · 0.5 °dH · 0.9 °fH).
Source: Ministério da Saúde, SISAGUA – controle semestral (Aguas Do Rio 4 Spe Sa), CC BY-ND 3.0 (2025) · data checked 2026-10-20
Range across supply zones: 6–12 mg/L.
Duque de Caxias is in the area served by the Guandu treatment plant in Nova Iguaçu, which draws on the Guandu River, itself fed largely by water transferred from the Paraíba do Sul. Records for 2025 give a median of 9.1 mg/L CaCO₃, with individual results from 5.8 to 12.4 mg/L. Limescale is rarely a problem at this level, and descaling the kettle is seldom necessary.
Portaria GM/MS nº 888/2021 sets a maximum of 300 mg/L CaCO₃ for total hardness (dureza total); operators report it in mg/L to SISAGUA.
Water data
| Total hardness | 9 mg/L |
|---|---|
| Utility | Aguas Do Rio 4 Spe Sa |
How Duque de Caxias compares
- Tap water in Duque de Caxias is 79 % softer than the median of the 1915 cities we track in Brazil (43 mg/L).
- By hardness it ranks 1831 of 1915 in Brazil (1 = hardest); 4 % of these cities have softer water.
- In Rio de Janeiro it is number 34 of 44 cities; the regional median is 14 mg/L.
- Nearest city with clearly softer water: Miguel Pereira, 23 km away (6 mg/L).
- Nearest city with clearly harder water: São João de Meriti, 17 km away (26 mg/L).
Ranking of the hardest and softest water in Brazil →
What it means at home
- Little or no limescale in kettles, water heaters or washing machines.
- Soap lathers easily; water does not dry skin or hair.
- Dishwasher: salt setting at minimum or off.
- No softener needed; a jug filter only changes taste.
How much salt will you use for softening?
No. Water this soft does not need softening.
Descale a coffee machine or kettle about every 6 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Duque de Caxias
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 1 °dH |
| AEG / Electrolux | 1 |
| Beko | 1st |
| Hoover | S0 |
| LG | H0 |
From each brand's manual for the model family named in the source; your model may differ, so check its manual. All brands and how to change the setting →
FAQ
Is Duque de Caxias water hard or soft?
It is soft: 9 mg/L as CaCO₃ (0.5 gpg, 0.5 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Duque de Caxias safe to drink?
Hardness is not a health issue; it is about limescale, taste and appliances. Mains water must meet national drinking-water standards. Portaria GM/MS nº 888/2021 sets a maximum of 300 mg/L CaCO₃ for total hardness (dureza total); operators report it in mg/L to SISAGUA.
How many grains per gallon is Duque de Caxias water?
0.5 gpg, equal to 0.5 °dH, 0.9 °fH or 9 mg/L calcium carbonate.
What dishwasher salt setting should I use in Duque de Caxias?
For 9 mg/L (0.5 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Duque de Caxias?
No. With soft water a softener adds nothing.
Source
Source: Ministério da Saúde, SISAGUA – controle semestral (Aguas Do Rio 4 Spe Sa), CC BY-ND 3.0 (2025). Method: figure published by the water supplier. Ministério da Saúde, SISAGUA – controle semestral (Aguas Do Rio 4 Spe Sa), CC BY-ND 3.0 · Outdated figure? Tell us