Sizing a Water Softener for Well Water
Special considerations for sizing softeners when you have iron, manganese, or tannins.
Well water adds complexity
Well water often contains iron, manganese, hydrogen sulfide, and tannins in addition to hardness minerals. These contaminants use up softener resin capacity and can foul the resin bed if levels are too high. Standard sizing formulas need adjustment.
The adjusted formula
Start with the standard calculation: (people × 75 gallons × GPG) × 7 days. Then add: 5 GPG for every 1 PPM of iron detected. 5 GPG for every 1 PPM of manganese. Example: 4 people, 20 GPG hardness, 2 PPM iron = (4 × 75 × 30) × 7 = 63,000 grains/week. You would need a 64,000-grain system.
Iron limits
Standard water softener resin handles iron up to 2-3 PPM. Above that, you need a dedicated iron filter upstream of the softener. Fine mesh resin handles up to 5-8 PPM iron but is more expensive. See our iron treatment guide.