The most important thing in the selection of a water softener is the matching of the actual demand of water with the quality of the raw water but also the continuity of water supply, the installation conditions and the operating costs. And it should be taken into fully consideration from four aspects, i.e. water quality parameters, water demand, equipment configuration and site conditions. Here are some selection factors you can start using now, in order of importance (with some practical tips):
I. Basic Water Quality Parameters (Pre-Testing for Model Selection Required)
Total hardness of raw water
The principal signal. Often reported in mmol/L and mg/L (CaCO3) (calculated as CaCO3) Requires a good test for the basic hardness of municipal/ground water.
The required resin loading increases with increasing hardness, and the volume of the salt tanks and regeneration frequency increases.
Other major indexes
Turbidity: Not more than 5 NTU The turbidity should be low otherwise a pre-filter with quartz sand will be necessary to avoid fouling of the resin with impurities.
Free chlorine: not more than 0.3 mg/l. Residual chlorine will oxidise and degrade cations.
Iron / manganese - Total iron 0.3 mg/L, manganese 0.1 mg/L. Iron and manganese ions can poison the resin. The resin can lose its exchange capacity. If the level is above standard, an iron and manganese removal filter is needed.
Water pH: 6 – 9 (optimal range of ion exchange resin performance) If water is too acidic or alkaline, its quality should be adjusted.
II. Equipment part, real water consumption
Maximum water delivered per hr
The model was computed with the maximum flow rate (not the average flow rate) in m3/h, which directly impacts the diameter of the water softener tank, the height of the resin bed, and the control valve characteristics in order to avoid low flow rate of water and high hardness during the maximum flow rate period.
Total Water Usage / Day / Month
Select the operating capacity of the resin according to the hardness of the raw water and set the regeneration cycle (time/flow rate) so that regeneration is not too frequent (increasing the operating costs) nor the time between regenerations too long (saturation of the resin).
Water demand over the long term
In case you don't need continuous water supply (small shops or houses for example): choose one automatic water softener tank. There will be some short water outages for the regeneration.
Buy a water softener with 2 tanks. One is in operation and the other is in reserve. For industries such as boilers, hotels, hospitals and chemical plants, water is required 24 hours a day, all the time. The two tanks are alternated in service and regeneration thus providing a continuous supply of soft water.
For ultra high flow rates (e.g. large industrial parks and thermal power plants): multi-tank parallel water softener system is suitable.
Hard water needs
The use case is compliance standards The different requirements of each of these situations affect the choice of resin and regeneration parameters.
For household use (whole house soft water, laundry) <=0.03mmol/l (national standard compliance)
Boiler feed water (low pressure) ≤0.03mmol/L, medium and high pressure boilers (pure water equipment can be used);
Industrial Pretreatment (electronics/pharmaceuticals) Pretreatment to pure/ultrapure water <0.01mmol/L
Selecting a Resin and Tank
For general civilian/industrial use, the best cost performance is the strong acid styrene based cation exchange resin 001×7, cation exchange resin. For high requirement applications, food grade resin can be chosen.
Tank material: Fibreglass (FRP preferred) (corrosion resistant, light weight, economical, good for general water quality) Optional carbon steel with rubber lining for corrosive environment/304/316 stainless steel for food/pharmaceutical industry. The tank diameter and the resin bed height should match the water production capacity and the resin bed height is usually ≥800mm to ensure adequate exchange.
Salt Tank and Regeneration Process
Material of salt tank: All PE plastic (corrosion resistance, hard to scale) Volume is calculated by water production and raw water hardness. During regeneration, brine supply should be guaranteed;
Regeneration Methods: Co-current regeneration (simple construction, low cost, regeneration efficiency of the order of 70%, suitable for small equipment) Counter current regeneration (> 90% regeneration efficiency, saves salt and water, increases resin life, preferred for industrial/large scale commercial use)
IV. Equipment installation and operating conditions (for the prevention of equipment failure or malfunction)
Location of installation
Tank footprint and height (diameter/height) and salt tank . Allow for backwash of resin and maintenance of equipment. Sewage pipeline and regeneration pipeline space layout.
Water inlet pressure and temperature
The best working conditions of the ion-exchange resin are: Water Pressure: 0.2-0.6Mpa. If the water pressure is too low you will have to fit a booster pump if it is too high you will have to fit a pressure reducing valve. Water temperature 5-45℃ Low water temperature will make the resin exchange effect not good, high water temperature will make the resin ageing and failure.
Conditions of power supply and sanitary sewer disposal
The automatic water softeners shall be connected to the 220V/380V AC mains power supply (as per the control valve specifications) and the site shall have stable power supply.
The equipment makes waste water (salt water, rinsing water) during regeneration. The wastewater discharge pipeline should be kept and the discharge port should not be back pressure in order to prevent backflow to the wastewater.
Costs of operation and maintenance (O&M)
Initial investment 2 tanks > 1 tank, Intelligent control valve > Flow type > Time type, Stainless steel tank > FRP tank
Operational costs are mainly industrial salt (iodized salt is strictly forbidden) and tap water (for backwash/forward wash/salt tank refill). Countercurrent regeneration needs about 30% less salt and water than cocurrent regeneration.
Maintenance cost: Replacement cycle of resin (generally 3-5 years, can be extended to 6-8 years in good water quality) and the difficulty and fragility of the replacement of control valve parts.
V. Additional considerations
Scenario characteristics
Food / Drinking water Industry: Food grade resin and stainless steel tanks are required and food hygiene standards must be met.
Outdoor installation: sunproof and frostproof tanks and salt boxes. "You have to insulate the equipment in the winter in the north.
Optional Small All in One Water Softener (Tank + Brine Tank) for Portable Use
Brand & after sales service
Make sure to select well known brands so that the basic components like control valves and water distributors are easily available and the manufacturers are able to provide after sales support like adjustment of regeneration parameters, recovery of resins and repair of faults.
Practical Core Formula Reference When Choosing Products
Resin loading (m3) = Water produced (m3/h) x Raw water hardness (mmol/L) x Working time (h)/Resin working exchange capacity (mol/m3)
The 001x7 resin in the standard form has an effective exchange capacity of 800-1000 mol/m3.
I will show you how to calculate the water softener tank specs, amount of resin fill and brine tank volume from 3 data points 1.
1. Raw water hardness
2. Water production per hour
3. Is there a continuous water supply? Is that what you want to do?
