Point of Use Filter Selection and Installation

Purpose

A point-of-use device is certified to reduce a named contaminant, under a named standard, for a stated number of gallons. Sell one without knowing which contaminant, and the shop has installed a device that may reduce nothing the customer is worried about. Two failure modes follow the sale rather than the install: a health claim runs out silently, with no taste change to announce it, and an unlisted connection turns a filter into a cross-connection. This procedure ties the device to a result, the interval to the household's real draw, and the connection to the plumbing code.

Scope

Covers selecting and installing an under-sink or countertop drinking water device - carbon block, lead reduction cartridge, or reverse osmosis - at a house, duplex, small retail unit, small restaurant or office.

Does not cover whole-house treatment, sized and placed under the whole house filtration installation SOP. Does not cover water softening or ion exchange. Does not cover the complaint diagnosis that decides whether a device is even the right answer, owned by the water quality complaint visit and taste and odor SOPs. Does not cover any claim that a device makes microbiologically unsafe water safe, which is not a plumbing decision.

Roles and responsibilities

Procedure

1. Refuse to select a device without a named target. Acceptance: a laboratory result or the water system's consumer confidence report naming the contaminant and its concentration, or a written aesthetic-only objective the customer has agreed to. What wrong looks like: a cartridge chosen off a complaint sentence, which cannot be checked against any certification. Stop rule: water that is microbiologically unsafe or of unknown quality is not a filter job; it routes to the health authority and a certified laboratory, and no device is offered as a fix in the meantime. Hazard: none here, it is a desk decision, and the discipline is verbal - the shop never states that a device makes unsafe water safe.
2. Match the standard to the claim, and verify the listing for that model. NSF/ANSI 42 covers aesthetic effects such as chlorine taste, odor and particulate; 53 covers health effects including lead and cysts; 58 covers reverse osmosis systems; 401 covers incidental and emerging compounds; 61 and 372 cover the materials and the lead content of the components themselves. Acceptance: the model number and the specific claim both found in the certifier's own listing, printed or screenshotted onto the job file. What wrong looks like: a box that says "NSF certified" with no standard and no claim, which is a materials listing at best. Stop rule: a claim not in the listing is not sold as a claim. Hazard: none at this step, a records check made before anything is ordered.
3. Size the interval to the household's actual draw, not to the label alone. Acceptance: the rated capacity in gallons read from the label, the household's drinking and cooking draw measured or logged in gallons per day, and the interval set as the shorter of capacity divided by draw and the labeled time interval. What wrong looks like: relying on taste to signal change-out, which works for a chlorine claim and fails silently for a lead or cyst claim, where nothing changes at the tap when the media is spent. Stop rule: where the computed interval is much shorter than the label's, the label does not win, and a household drawing far above the assumption is told before the device is fitted. Hazard: none here, but the interval is what the whole device depends on, so it goes on the housing and on the customer record the same day.
4. Check the connection before drilling anything. Acceptance: all wetted components lead free as the Safe Drinking Water Act defines it, a weighted average of not more than 0.25 percent lead across the wetted surfaces, with NSF/ANSI 372 as the conformance route; the device fed from a cold supply only; and a proper quarter-turn or compression stop rather than a piercing saddle valve. What wrong looks like: a hot or tempered feed, which destroys a carbon block, deforms plastic housings and voids the certification the sale rested on. Stop rule: a piercing saddle valve found on site is replaced with a listed stop, not reused, and the device is not commissioned until it is. Hazard: close the stop and open the fixture until flow stops before breaking any connection - a saddle valve removed under line pressure sprays across a cabinet at face height.
5. Mount and plumb it so the next cartridge change is a five minute job. Acceptance: the housing supported by its bracket and not by the tubing, with clearance below for the sump to swing down; tubing routed clear of drawer travel and secured; the shutoff reachable without emptying the cabinet; and a drip path that lands where a leak is visible rather than under a cabinet floor. What wrong looks like: a housing screwed to the underside of a countertop with no swing clearance, which guarantees the interval is missed. Stop rule: if the clearance is not there, the device is relocated rather than fitted tight. Hazard: drilling a cabinet or a sink deck throws chips toward the face, so wear eye protection and clamp or back the work, and check what is behind the panel before the bit goes through.
6. On a reverse osmosis unit, treat the drain connection as cross-connection control and set the tank from its label. Acceptance: the reject line discharged through an air gap, either an air-gap faucet or an air-gap fitting, as the adopted plumbing code requires for indirect waste in the edition your jurisdiction enforces; feed pressure measured and at or above the manufacturer's stated minimum; and the storage tank pre-charge measured with the tank isolated and drained and corrected to the value printed on the tank. What wrong looks like: a drain saddle tapped into the trap arm with no air gap, which is a direct connection between drainage and a drinking water device. Stop rule: no air gap, no commissioning. Hazard: check pre-charge only with the tank isolated and fully drained, since a charged bladder against a full tank reads high and gauging a pressurized vessel can unseat the valve core into your hand.
7. Sanitize, purge and start up under one chemistry. Acceptance: the housing and tubing sanitized per the manufacturer's instruction, the system purged for the manufacturer's stated volume or duration until the water runs clear of carbon fines, and on a reverse osmosis unit the first tank fills discarded as the instruction directs. What wrong looks like: a first glass poured for the customer full of black fines. Stop rule: fines still visible at the end of the stated purge means the purge continues and the extra volume is recorded, rather than the customer being told it will clear. Hazard: use one chemistry and flush it completely - a chlorine sanitizer meeting an acid descaler releases chlorine gas, an inhalation hazard in a closed cabinet, so ventilate the space, keep the products apart on the van, and wear the gloves and eye protection the safety data sheets specify.
8. Repressurize, leak check, prove the protective functions and label the device. Acceptance: the stop opened slowly with the faucet open to bleed air, then a hold at full line pressure for a stated period with every joint dry to a paper towel; the stop confirmed to close fully and reopen; the air gap observed discharging to atmosphere with a visible break; the housing marked with the install date and the next change date; and a written note to the customer naming the certified claim and what the device does not cover. What wrong looks like: a hand-tight fitting signed off after thirty seconds of dry pipe. Stop rule: any weep at the hold is remade, not tightened further, and the hold restarts. Hazard: this puts full line pressure back inside a closed cabinet with the customer alongside, so open the stop slowly, keep your face out of line with the housing seam, and stay clear of the sump while it comes up to pressure.

The record this produces

One device record on the customer file: the lab result or water quality data that justified the selection; the model number, the standard and the exact certified claim, with the listing evidence attached; the capacity read from the label; the measured daily draw and the interval computed from it alongside the labeled interval, with the governing one marked; the connection type replaced or installed; the reverse osmosis air gap method and the tank pre-charge as found and as set; the purge volume; the pressure hold result; and the written note handed to the customer.

The interval line is the one that comes back. A year later, when someone asks whether the cartridge is due, the answer is on that record with the arithmetic behind it, and the shop can defend why it is not the six months printed on the box.

One worked pass, including a failure

Duplex, one unit, laboratory result on file showing lead present in a first draw collected under the sampling SOP. Target named at step 1: lead reduction at the kitchen cold tap. Step 2: a reverse osmosis system listed under NSF/ANSI 58 with a lead reduction claim, and its pre-filter listed under 53 for lead; both model numbers and both claims found in the certifier's listing and printed to the file.

Step 3: label capacity read as 170 gal for the lead claim. The household logs drinking and cooking draw over a week and averages 2.5 gal per day, so 170 divided by 2.5 is 68 days. The labeled interval is 6 months, roughly 180 days, so the computed interval governs and the change is set at 2 months. The customer is told at the estimate rather than at the first change.

Step 4 fails. The existing under-sink filter is fed by a piercing saddle valve clamped to the cold supply, and the old unit's reject line is tied into the trap arm below the trap with no air gap. Stop rule taken: the device is not commissioned. The saddle valve is removed after closing the angle stop and running the faucet down, a listed quarter-turn stop is installed on the cold supply, and the drain tie is abandoned.

Steps 5 through 8: housing bracketed with sump swing clearance, tubing clear of the drawer, shutoff reachable. Static feed pressure measured at 55 psi against a manufacturer minimum of 40 psi, so the unit runs without a booster. Air-gap faucet fitted and the reject routed through it. Tank pre-charge measured with the tank isolated and drained reads 4 psi against the 7 psi printed on the tank, and is corrected to 7. Sanitized and purged per the instruction, first two tank fills discarded, water clear of fines at the end of the stated purge. Stop reopened slowly with the faucet open, 20 minute hold at full line pressure, every joint dry to a paper towel, stop cycled closed and open, air gap seen discharging with a visible break. Housing dated, next change dated two months out, and the customer handed a note naming the lead claim and stating that the unit is not a treatment for unsafe water.

References

• NSF/ANSI 42, 53, 58, 401, 61 and 372, and the certifier's own public listing for the specific model and claim; certification is per model and per claim, not per brand.
• Safe Drinking Water Act lead-free definition, a weighted average of not more than 0.25 percent lead of the wetted surfaces, as amended by the Reduction of Lead in Drinking Water Act.
• The adopted plumbing code's indirect waste and air gap requirements, in the edition your jurisdiction enforces, for the reverse osmosis reject connection.
• Manufacturer instructions for feed pressure minimum, tank pre-charge, purge volume and sanitizing, plus the safety data sheet for any sanitizer used.
• See related: the Plumbing whole house filtration installation SOP, the water sample collection SOP, and the taste and odor complaint investigation SOP.