1 Scope
NOTE This standard covers the selection, sizing, construction, controls, installation, and commissioning of point-of-entry water treatment equipment that conditions the domestic cold-water supply before it is distributed through the building. (1.1)
NOTE Covered equipment includes the following equipment types, used singly or assembled into a combination treatment train: (1.2)
- Cation-exchange water softeners regenerated with sodium chloride or potassium chloride.
- Multimedia pressure filters for sediment and turbidity reduction.
- Cartridge sediment filters in single or manifolded housings.
- Granular activated carbon (GAC) filters for chlorine, taste, and odor reduction.
- Point-of-entry reverse-osmosis (RO) skids for total-dissolved-solids (TDS) reduction.
- Salt-free scale conditioners (template-assisted crystallization and polyphosphate feeders).
- Ultraviolet (UV) disinfection units used as a final stage on well-water trains.
NOTE The work extends from the cold-water service connection downstream of the building's backflow protection, through the treatment equipment, its bypass, its brine and backwash drain connections, and its controls, to the conditioned-water connection feeding the building domestic distribution. (1.3)
NOTE The incoming backflow assembly at the point of connection, the conditioned-water distribution piping, the domestic booster pumps, and the water heaters are each governed by their own standard and are coordinated with, but not specified by, this standard. (1.4)
NOTE Process water, cooling-tower makeup, boiler feedwater, and ultrapure/laboratory water systems are excluded; treatment of those systems is governed by
Hvac Water Treatment and the applicable process discipline.
(1.5) 2 Treatment Objective
NOTE The treatment objective is the first decision the design must resolve, because it determines equipment type, certification basis, and whether the system removes a contaminant or merely conditions the water. (2.1)
NOTE Softening removes hardness ions (calcium and magnesium) by ion exchange; sediment filtration removes turbidity and particulates; carbon filtration reduces chlorine, taste, and odor; RO reduces dissolved solids; and scale conditioning inhibits scale crystallization without removing any ion. These outcomes are not interchangeable. (2.2)
2.3The treatment objective shall be stated explicitly in the Contract Documents so that a scale-conditioning device is not substituted where actual hardness-ion removal is required for code compliance or equipment warranty.
2.4Where downstream water heaters or hydronic equipment carry a warranty conditioned on softened water, the system shall remove hardness ions to the maximum hardness limit stated in that warranty rather than merely inhibiting scale.
☑ Hardness removal (softening)
☐ Sediment / turbidity removal
☐ Chlorine, taste, and odor reduction
☐ Health-contaminant reduction (lead, cysts, VOCs, nitrate, arsenic)
☐ TDS reduction (reverse osmosis)
☐ Microbiological disinfection (UV)
☐ Scale inhibition without hardness removal
3 Referenced Standards
3.1Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited or a different edition is enforced by the authority having jurisdiction.
3.2Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
| Standard |
Title |
| NSF/ANSI 44-2024 |
Residential Cation Exchange Water Softeners |
| NSF/ANSI/CAN 61-2025 |
Drinking Water System Components — Health Effects |
| NSF/ANSI 42 |
Drinking Water Treatment Units — Aesthetic Effects |
| NSF/ANSI 53 |
Drinking Water Treatment Units — Health Effects |
| NSF/ANSI 58 |
Reverse Osmosis Drinking Water Treatment Systems |
| NSF/ANSI 55 |
Ultraviolet Microbiological Water Treatment Systems |
| NSF/ANSI 372 |
Drinking Water System Components — Lead Content |
| 2021 IPC |
International Plumbing Code, Chapter 6 — Water Supply and Distribution |
| 2021 UPC |
Uniform Plumbing Code, Chapter 6 — Water Supply and Distribution |
| WQA S-100 |
Water Quality Association Standard for Softeners |
| ASTM D2473 |
Styrene-Divinylbenzene Cation Exchange Resin |
NOTE The NSF/ANSI 44 scope is nominally limited to residential cation-exchange softeners, but the standard is universally applied to commercial submittals and commercial-scale units are certified to it in practice; certification to NSF/ANSI 44 is therefore required for cation-exchange softeners regardless of project scale. (3.3)
4 Submittals
4.1The Contractor shall submit the following Action Submittals for review before fabrication or ordering:
- Product data for each treatment unit, including rated capacity, service flow rate, pressure drop curve, and connection sizes.
- Certification listings confirming NSF/ANSI compliance for each unit and each wetted component (NSF/ANSI 44, 42, 53, 58, 55, 61, and 372 as applicable).
- Sizing calculations showing incoming hardness, daily demand, grains-per-day load, selected salt dose, and resulting regeneration frequency.
- Brine and backwash discharge calculations, including peak backwash flow and required air-gap dimension.
- Control sequence and BMS interface point list, including salt-low alarm, fault, and flow-meter pulse output.
- Wiring diagram and electrical load for each electronic control head.
☑ Product data for each treatment unit
☑ NSF/ANSI certification listings (wetted components)
☑ Sizing calculations (hardness, demand, salt dose, regen frequency)
☑ Brine / backwash discharge and air-gap calculations
☐ Control sequence and BMS point list
☐ Wiring diagram and electrical load data
4.2The Contractor shall submit the following Closeout Submittals before Substantial Completion:
- Operation and maintenance manuals for each unit, including regeneration setup, media replacement intervals, and salt specification.
- A media and cartridge replacement protocol identifying spent-carbon handling and change-out frequency.
- Commissioning report documenting hardness, chlorine, and pressure-drop test results before and after treatment.
- Warranty documents for resin, media, control valves, and electronic heads.
☑ Operation and maintenance manuals
☑ Media and cartridge replacement protocol
☑ Commissioning report (before/after water quality)
☑ Warranty documents
4.3The Contractor shall submit the following Informational Submittals:
- An on-site or laboratory water-quality analysis of the incoming supply used as the sizing basis.
- The local sewer authority discharge limits or permit applicable to regeneration brine, where chloride discharge is restricted.
☑ Incoming water-quality analysis (sizing basis)
☐ Brine discharge limits / municipal permit documentation
5 Quality Assurance
5.1All wetted components in potable service — resin, filter media, valve bodies, tanks, and fittings — shall be certified to NSF/ANSI/CAN 61 for health effects.
5.2Components in potable service shall comply with NSF/ANSI/CAN 61 for chemical leaching.
5.3Wetted metallic components shall comply with the lead-content limits of NSF/ANSI 372.
5.4Cation-exchange softeners shall be certified to NSF/ANSI 44.
5.5Carbon and sediment filters specified for aesthetic reduction shall be certified to NSF/ANSI 42.
5.6Filters specified for health-contaminant reduction shall be certified to NSF/ANSI 53.
5.7Reverse-osmosis units shall be certified to NSF/ANSI 58.
5.8Ultraviolet disinfection units shall be certified to NSF/ANSI 55.
5.9Ion-exchange resin shall be styrene-divinylbenzene cation-exchange resin conforming to ASTM D2473.
NOTE NSF/ANSI 44 rated grain capacities are established at the maximum salt dose; a unit's catalog capacity is therefore not the capacity it will deliver at an efficient salt dose, and the two must not be confused during selection. (5.10)
6 Environmental and Service Conditions
NOTE Ion-exchange resin and filter media are temperature-sensitive and freeze-intolerant, which constrains where the equipment may be installed and which line it may serve. (6.1)
6.2Treatment equipment shall be installed on the cold-water supply only, upstream of all water heaters and hydronic heat sources.
6.3Treatment equipment shall not be installed on a hot-water line or downstream of a water heater, because cation-exchange resin degrades above 110°F (43°C) and softening performance is lost.
6.4Equipment shall be located in a conditioned space; where freezing is possible, a heat-traced and insulated enclosure shall be provided, because resin tanks and valve assemblies are not freeze-tolerant.
6.5The equipment shall be sized and rated for the service conditions in the datasheet below.
20125
2060125
Default: 60 psi
40-100°F (4-38°C) — standard resin/media service
40-80°F (4-27°C) — cold-climate well supply
6.6The equipment shall be located within reach of a gravity-accessible floor drain sized for backwash surge flow, and within 6 ft (1.8 m) of a dedicated 120 VAC receptacle or junction box for the electronic control head.
7 Softener Selection and Configuration
NOTE Softener configuration is governed by three coupled decisions — softener chemistry, single versus twin tank, and regeneration control — each of which is set independently by the application. (7.1)
7.2Softener chemistry shall be selected to match the treatment objective: sodium-chloride cation exchange for general hardness removal, potassium-chloride cation exchange where low-sodium effluent is required, and salt-free conditioning only where scale inhibition without ion removal is acceptable.
7.3Potassium-chloride regeneration shall be specified where sodium-sensitive occupants or processes — dialysis, certain food production — require reduced sodium in the effluent.
7.4Salt-free template-assisted crystallization (TAC) and polyphosphate conditioners do not remove hardness ions and cannot be certified to NSF/ANSI 44; they shall not be substituted where the Contract Documents require hardness-ion removal.
● Sodium-chloride cation exchange
○ Potassium-chloride cation exchange (low-sodium effluent)
○ Salt-free TAC (scale inhibition only)
○ Polyphosphate feeder (scale inhibition only)
NOTE A single-tank softener is offline during regeneration and delivers hard water through the bypass during that interval; a twin/duplex alternating system keeps one tank in service while the other regenerates and therefore delivers continuous soft water. (7.5)
7.6Facilities requiring continuous soft water — 24/7 healthcare, food service, and hospitality — shall be served by a twin/duplex alternating softener or a hard-water bypass arrangement that maintains service during regeneration and maintenance.
● Single tank (regenerates offline)
○ Twin / duplex alternating (continuous soft water)
NOTE Regeneration control determines when the unit regenerates: a time-clock regenerates on a fixed calendar regardless of use, while a demand-initiated meter regenerates only after a measured volume has been treated, matching salt and water use to actual demand. (7.7)
7.8Commercial and institutional softeners shall use demand-initiated (meter-initiated) regeneration control; time-clock (calendar) control shall not be used for any facility with variable occupancy.
● Demand-initiated (metered)
○ Hardness-sensor-triggered
○ Time-clock (residential only)
8 Softener Sizing and Salt Efficiency
NOTE Softener sizing reconciles three quantities — the hardness load, the salt dose, and the regeneration frequency — and the most common sizing error is to select on catalog capacity without resolving the salt-dose efficiency trade-off. (8.1)
8.2Incoming hardness shall be established from a current water-quality analysis and stated in grains per gallon (gpg), where 1 gpg equals 17.1 mg/L as CaCO3.
8.3The softener shall be sized so that the grains-per-day load — incoming hardness in gpg multiplied by daily demand in gallons — does not require regeneration more frequently than every three days, with a commercial design target of approximately seven days between regenerations at an efficient salt dose.
NOTE Salt dose is the trade-off between efficiency and capacity: 6 to 8 lbs/ft³ of resin yields roughly 2,000 to 2,500 grains removed per pound of salt, while 15 lbs/ft³ reaches the catalog rated capacity at roughly 3,200 grains per pound but with sharply diminishing efficiency above 8 lbs/ft³. (8.4)
8.5The design salt dose shall be 6 to 8 lbs/ft³ of resin for efficient operation unless a specific application justifies a higher dose.
8.6The salt dose shall not exceed 15 lbs/ft³ of resin.
8.7Capacity selected against an NSF/ANSI 44 rated capacity shall be derated by 35% to 40% to reflect efficient salt-dose operation when comparing units.
325
3101425
Default: 10 gpg
615
6815
Default: 6 lbs/ft³
24,000 grains
32,000 grains
48,000 grains
64,000 grains
96,000 grains
120,000 grains
150,000 grains
8.8The softener shall be sized for the peak instantaneous service flow, and the pressure drop across the softener shall not exceed 15 psi at the design service flow.
580
10204080
Default: 20 GPM
8.9The brine tank shall hold at least a 30-day supply of salt between fills at the design regeneration frequency.
200500
200300500
Default: 300 lbs
9 Pre-Filtration and Post-Treatment
NOTE Pre-filtration protects the resin bed, and post-treatment adds the carbon, RO, or UV stages required by the treatment objective; both are arranged in series with the softener in a defined order. (9.1)
9.2A sediment pre-filter rated at 5 µm or finer shall be installed upstream of the softener resin bed to prevent turbidity and iron from fouling the resin and voiding the warranty.
9.3The sediment pre-filter shall be replaced per the manufacturer's schedule or when the differential pressure across it exceeds 15 psi, whichever occurs first.
○ Cartridge, 5 µm, 10-inch housing
● Cartridge, 5 µm, 20-inch housing
○ Cartridge, 1 µm, 20-inch housing
○ Multimedia pressure filter (sand/anthracite/garnet)
9.4Where chlorine, taste, or odor reduction is required, a granular activated carbon (GAC) filter shall provide a minimum empty-bed contact time (EBCT) of 5 minutes at the rated flow.
9.5Granular activated carbon can harbor bacteria once exhausted; the Contract Documents shall establish a media change-out interval, and spent carbon shall be handled per the O&M protocol.
☑ GAC carbon filter (chlorine / taste / odor)
☐ Reverse-osmosis skid (TDS reduction)
☐ UV disinfection (well water)
☐ None
9.6Where TDS reduction is required at point of entry, a reverse-osmosis skid certified to NSF/ANSI 58 shall be provided with a permeate storage tank and repressurization.
9.7Point-of-entry RO shall be specified only for very high TDS or special-use applications.
NOTE Point-of-use RO is preferred for isolated demands. (9.8)
9.9Where well water requires microbiological treatment, a UV disinfection unit certified to NSF/ANSI 55 shall be provided as the final stage at a minimum dose of 30 mJ/cm² at the rated flow.
1640
163040
Default: 30 mJ/cm²
10 Bypass, Connections, and Sampling
NOTE A maintainable treatment system requires an accessible bypass, correctly sized connections, and sampling ports that let the commissioning agent and operator verify performance. (10.1)
10.2A full-port bypass shall be provided — factory-integrated three-valve bypass or field-installed full-port ball valves — so that the equipment can be isolated and the building served while a unit is out of service.
10.3The bypass and service valves shall be accessible per IPC Section 605.4 service-access requirements, and the bypass shall be labeled.
10.4Sampling ports shall be provided immediately upstream and downstream of each treatment stage to permit verification of treatment performance.
● Factory-integrated three-valve bypass
○ Field-installed full-port ball valve bypass
3/4 inch FNPT
1 inch FNPT
1-1/2 inch FNPT
2 inch FNPT
2-1/2 inch flanged
3 inch flanged
10.5A backflow preventer shall be provided on the supply upstream of the treatment equipment; the assembly type and location are specified in Backflow Prevention. NOTE The backflow prevention assembly is governed by
Backflow Prevention and is not specified here to avoid double-specification.
(10.6) 11 Brine and Backwash Discharge
NOTE The brine and backwash discharge is both a code item and a coordination item: it must be drained through an air gap, sized for backwash surge, and reconciled with local limits on chloride discharge. (11.1)
11.2The brine and backwash drain connection shall discharge through an air gap to the receiving drain in accordance with IPC/UPC Table 603.3.1; a direct connection to the drainage system is prohibited.
11.3The air gap shall be at least twice the drain pipe diameter, and not less than the minimum required by Table 603.3.1; a 1-inch drain therefore requires a minimum 2-inch air gap.
11.4The backwash drain line shall be sized for the peak backwash flow, which can reach approximately 5 GPM per ft³ of resin, and the receiving floor drain shall be verified to accept that surge.
NOTE Regeneration brine can carry 50,000 to 100,000 mg/L of chloride, and some municipalities restrict chloride discharge to the sanitary sewer. (11.5)
11.6The Contractor shall verify the local sewer authority's chloride discharge limits and obtain any required discharge permit before regeneration is placed in service.
11.7The drain, brine-tank overflow, and floor drain locations shall be coordinated with the sanitary drainage design.
NOTE The receiving interceptor and drainage are governed by
Grease Interceptors and the project plumbing drawings.
(11.8) 12 Controls and Monitoring
NOTE Commercial treatment systems are monitored points on the building management system, and omitting the integration outputs is a common source of RFIs late in the project. (12.1)
12.2Each electronic control head shall provide a local display of service status, remaining capacity, and fault condition.
12.3The softener controller shall provide a hardwired salt-low alarm output and a general fault output to the building management system.
12.4The softener controller shall provide a flow-meter pulse output for water-use reporting.
☑ Local display (status / capacity / fault)
☑ BMS salt-low alarm (hardwired)
☑ BMS general fault (hardwired)
☑ Flow-meter pulse output
☐ Hardness-sensor output
12.5The control head shall be powered from 120 VAC, 60 Hz.
12.6Remote monitoring connections requiring 24 VDC or a LAN connection shall be coordinated with the electrical and controls work.
120 VAC, 60 Hz, 1Φ
120 VAC head + 24 VDC monitoring
120 VAC head + LAN connection
13 Materials
NOTE Treatment-equipment materials are constrained by potable-water certification and by the mechanical service of each component. (13.1)
13.2Resin tanks shall be fiberglass-reinforced or polyethylene-lined pressure vessels rated for the service pressure and certified to NSF/ANSI/CAN 61.
13.3Brine tanks shall be high-density polyethylene with a salt platform or brine-well as applicable.
13.4Control valve bodies shall be lead-free brass or engineered polymer certified to NSF/ANSI/CAN 61 and NSF/ANSI 372.
13.5Ion-exchange resin shall be styrene-divinylbenzene cation-exchange resin conforming to ASTM D2473 and certified to NSF/ANSI/CAN 61.
● Fiberglass-reinforced composite
○ Polyethylene-lined steel
○ Lead-free brass (NSF 61 / 372)
● Engineered polymer (NSF 61)
14 Testing and Commissioning
NOTE Commissioning proves the treatment objective was met by measuring water quality before and after treatment, not merely by confirming the equipment runs. (14.1)
14.2The Contractor shall measure and record incoming and treated hardness; treated hardness shall meet the design target and any limit imposed by a downstream equipment warranty.
14.3Where carbon filtration is provided, the Contractor shall measure and record free-chlorine reduction across the carbon stage at the rated flow.
14.4The Contractor shall record the pressure drop across each treatment stage at the design flow and confirm it is within the specified limit.
14.5A regeneration cycle shall be initiated and observed to confirm correct backwash, brine draw, and air-gap discharge with no overflow or leakage.
14.6New cation-exchange media shall be disinfected and the system flushed to waste before the treated water is placed in domestic service, in accordance with the manufacturer's start-up procedure.
☑ Incoming vs. treated hardness
☐ Free-chlorine reduction across carbon
☑ Pressure drop per stage at design flow
☑ Observed regeneration cycle and air-gap discharge
☑ Media disinfection and flush-to-waste
15 Installation
NOTE Installation places the equipment on the cold-water supply, downstream of backflow protection and upstream of the water heaters, with the bypass, drain, and clearances required for service. (15.1)
15.2The treatment equipment shall be installed on the cold-water service downstream of the building backflow protection and upstream of the water heaters and any hydronic heat source.
15.3Unions or grooved couplings shall be provided at the inlet, outlet, and bypass so that each unit can be removed without cutting piping.
15.4The equipment shall be set level on a housekeeping pad or manufacturer-approved base, with clearance maintained for media replacement, valve service, and brine-tank refilling.
15.5The brine and backwash drain shall be installed with the required air gap and pitched to the receiving floor drain.
15.6Treatment piping requiring insulation shall be insulated in accordance with Plumbing Insulation. NOTE Conditioned-water distribution downstream of the equipment is installed under
Domestic Water Piping.
(15.7) 16 Delivery, Storage, and Handling
NOTE Resin, media, and brine salt are sensitive to freezing, moisture, and contamination. (16.1)
16.2Resin, media, and brine salt shall be protected from the point of delivery to installation.
16.3Resin and filter media shall be delivered in the manufacturer's sealed packaging and stored in a clean, dry, conditioned space protected from freezing.
16.4Equipment shall be stored with all openings capped or plugged to prevent the entry of dirt, debris, and vermin until connection.
16.5Salt for the brine tank shall be water-softener-grade evaporated or solar salt as recommended by the softener manufacturer and shall be kept dry until use.
17 Warranty
NOTE The treatment-equipment warranty distinguishes the consumable media from the durable control and tank components, which carry different terms. (17.1)
17.2The Contractor shall provide the manufacturer's standard warranty for resin and filter media against premature loss of capacity under the specified service conditions.
17.3The Contractor shall provide the manufacturer's standard warranty for control valves, electronic heads, and pressure vessels.
1 year
3 years
5 years
10 years
18 Spare Parts
NOTE A treatment system consumes filter cartridges, media, and salt, and a defined initial stock keeps the system in service between maintenance visits. (18.1)
18.2The Contractor shall furnish one complete set of replacement sediment and carbon cartridges for each housing provided.
18.3The Contractor shall furnish one initial fill of brine salt sufficient for the first 30 days of operation at the design regeneration frequency.
☑ One spare set of sediment cartridges per housing
☑ One spare set of carbon cartridges per housing
☐ One spare UV lamp and sleeve (if UV provided)
☑ 30-day initial brine salt fill