How hard is my water?

UK water hardness varies hugely by region. London and the South East typically has very hard water (300+ ppm calcium carbonate). Scotland and the North West generally have soft water (under 100 ppm). Your water company publishes hardness data for your postcode area, or you can test with a simple strip test.

How is water softener capacity measured?

Softener capacity is measured in grains of hardness that the resin can remove before needing regeneration. One grain per gallon (gpg) equals 17.1 ppm. A typical domestic softener removes 4,000-10,000 grains between regenerations. Daily grain removal = hardness (gpg) × daily gallons used.

How often does a water softener regenerate?

Regeneration frequency depends on water hardness and usage. In a hard water area (250 ppm) with a 4-person household, a medium softener typically regenerates every 3-5 days. Each regeneration uses approximately 25 litres of water and 2 kg of salt.

How much salt does a water softener use?

A domestic water softener uses approximately 2 kg of block salt per regeneration. With regeneration every 3-5 days, annual salt consumption is typically 150-240 kg. Block salt costs approximately £5-7 per 8 kg pack, so annual salt costs are roughly £100-200.

Can I drink softened water?

Softened water is generally safe to drink, though it contains slightly elevated sodium levels. WRAS (Water Regulations Advisory Scheme) recommends maintaining one un-softened cold water tap for drinking and cooking, typically the kitchen cold tap. This is also a Building Regulations requirement.

TradeCalculator

Water Softener Calculator — Capacity & Salt Usage

Calculate water softener capacity from hardness (ppm) and daily usage. Determine regeneration frequency and annual salt consumption.

Water Hardness

Local water hardness level

Daily Water Usage

Total household water usage

Occupants

Number of people in household

How We Calculate This

This calculator determines the required water softener capacity based on your water hardness and daily consumption, then estimates regeneration frequency and annual salt usage.

Method

Hardness (gpg): ppm ÷ 17.1
Daily grains: gpg × daily gallons
Regen frequency: Softener capacity ÷ daily grains
Annual salt: Regenerations per year × kg per regen

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.