Methodology

Results are compared to published EPA drinking water standards. The distinction between the two kinds matters and we keep it explicit throughout.

• Primary standards (MCLs) are health-based and enforceable for public systems. Nitrate at 10 mg/L as N, arsenic at 0.010 mg/L, coliform bacteria absent.
• Secondary standards (SMCLs) are aesthetic. Iron 0.3 mg/L, manganese 0.05 mg/L, TDS 500 mg/L, sulfate and chloride 250 mg/L, pH 6.5 to 8.5.
• Private wells are regulated by neither. These are the right benchmarks to hold your water to, but nobody is enforcing them on your behalf.

• Hardness conversion: 1 grain per gallon = 17.1 mg/L as calcium carbonate.
• Household use: 75 gallons per person per day by default, adjustable in the tool.
• Iron and manganese compensation: 4 gpg of additional load per mg/L. The commonly published range is 3 to 5; we use the midpoint.
• Target regeneration interval: 7 days.
• Usable capacity: 75% of rated capacity, because ratings are measured at maximum salt dose.
• Iron limit for a softener alone: 3 mg/L, above which we recommend a dedicated iron filter.

• Salt efficiency: 4,000 grains of hardness removed per pound of salt at an efficient dose. At maximum dose this falls to roughly 2,500.
• Regeneration water: about 50 gallons per cycle.
• Water cost defaults to zero, because well owners pump their own — only the electricity is theirs to pay.

• Drawdown factors: 30% at 20/40 psi, 25% at 30/50 psi, 21% at 40/60 psi.
• Minimum pump run time: 1 minute below 1 HP, 2 minutes at 1 HP and above.
• Required drawdown = pump GPM x minimum run time; tank volume = drawdown / drawdown factor, rounded up to a standard size.
• Air pre-charge: 2 psi below cut-in pressure.

This is deliberately more precise than the widely repeated “tank = GPM x runtime x 1.5” rule, which ignores the pressure switch setting entirely even though that is what determines how much of the tank you can actually use.

Equipment cost ranges are planning figures compiled from published pricing for typical residential systems. They are not quotes and they are not based on our own purchasing. Installed cost varies widely with plumbing, water chemistry and region.

Nothing on this site is a substitute for a certified laboratory test or advice from a licensed professional. Where a result touches health — bacteria, nitrate, arsenic — the right next call is your county or state health department, not a website.