Water Level and Autofill Service
Purpose
An autofill is a device whose entire job is to hide a change in water level, which means it also hides a leak, hides itself when it fails, and quietly dilutes the water it is keeping topped up. A pool on a passing fill valve reads at the right level every week while the meter spins and the stabilizer walks downward, and the shop chases a chlorine that will not hold for a season. Worse, a fill spout sitting below the water surface with nothing protecting it is a direct connection between a chlorinated pool and the house drinking water. This procedure guarantees the level is measured against a fixed reference, the fill valve is proven to shut rather than assumed to, and the backflow protection on the fill line is checked before anyone services the valve behind it.
Scope
Covers operating water level, mechanical float-valve and solenoid autofills, the fill line's backflow protection, and the loss-rate measurement that separates evaporation from a leak, on residential and small semi-commercial pools.
It does not cover locating a leak once the loss is proven, which the leak detection visit standard owns, nor liner-specific losses, which the vinyl liner standard owns. It does not size or install a backflow assembly: that is a licensed plumber's work and this procedure's job is to notice when one is missing. Deliberate water removal is the partial drain and dilution decision.
Roles and responsibilities
| Role | Owns | Hands off |
|---|---|---|
| Route technician | The level reading, the bucket test, the fill valve shutoff proof, the chemistry drift read | Hands a missing or failed backflow finding to the service manager the same day, not at the next visit |
| Service manager | Plumber referral, the customer notification, whether the fill line stays shut off | Hands the customer the cross-connection finding in writing, because it concerns their drinking water, not their pool |
| Shop lead | The bucket-test cadence on autofilled accounts | Hands the leak-versus-evaporation verdict to the leak detection standard rather than guessing at it |
Procedure
Read the level against the skimmer mouth and record it before anything is adjusted. Note where the water sits as a fraction of the skimmer opening, and mark a fixed reference on the tile so the next technician reads the same datum. Accept the level as correct when it sits between one third and one half up the skimmer mouth. Wrong is water at or below the bottom lip, which lets the skimmer draw air and starves the pump, or water above the opening, which stops the weir working so nothing skims. Hazard is reading the datum from the coping edge on a wet deck, so kneel rather than lean, and keep the pole out of the overhead service drop while marking.
Isolate the autofill and run a bucket test whenever loss is in question. Close the fill line at its stop, set a bucket on a step with its inside level matched to the pool level, and read both on the same rule after at least 24 hours, preferably 48. Accept evaporation as the explanation when the pool drop and bucket drop agree within the resolution of your rule. Wrong is a comparison taken with the fill line still live, which produces a pool that did not move and a bucket that did. Stop and rerun it isolated. Do not skip the isolation because the valve "looks closed": the whole failure mode of this device is passing water while appearing shut.
Prove the fill line's backflow protection before servicing the valve behind it. Follow the fill line to its termination and confirm either a physical air gap above the pool's flood level or an approved backflow prevention assembly on the line, whichever the plumbing code your jurisdiction has adopted requires for this installation. Accept when one of those two is present and intact. Wrong is a fill spout or a garden hose ending below the water surface with nothing in between: that is a direct cross-connection, and a drop in street pressure can pull pool water back toward the house supply, which is an ingestion exposure to the people living there. Stop, close the fill stop, notify the service manager the same day so the customer is told, and route the correction to a licensed plumber and the water purveyor's cross-connection program. Do not service the valve behind an unprotected connection and leave the connection as you found it.
Open the valve box, clear it, and service the float valve. Look into the box before a hand goes in, because these are buried plastic boxes that collect spiders, wasps and broken irrigation debris, and clear it with a tool rather than fingers. Rebuild or replace the float valve to the manufacturer's kit: seat, diaphragm or washer, and pivot. Accept when the box is clear, the box drains rather than holding standing water, and the valve moves through its full travel without binding. Wrong is a box packed with soil and roots, which holds the float part-open permanently. Gloves stay on: standing water in a fill box is not potable and it is not clean.
Prove shutoff by drawing the level down and watching the valve close. Raise the float by hand and confirm flow stops, then lower the pool level below the setpoint, let it refill, and watch it stop on its own. Accept when flow stops completely at the setpoint with no drip at the outlet after 60 seconds and the level settles between one third and one half up the skimmer mouth. Wrong is a valve that slows but never fully closes, which is the failure that runs a meter and dilutes the pool without ever showing a wrong level. Replace it rather than adjusting it further, because a seat that will not seal does not improve with tension. Hazard at this step is standing water and a live hose in a deck box, so keep the hose end above the box rim.
Read the chemistry for the signature of a valve that has been passing. A fill valve weeping continuously dilutes, so stabilizer, calcium hardness and total alkalinity all drift toward the fill water's own numbers rather than staying where they were dosed. Accept the water as undiluted when stabilizer and calcium hardness sit within their expected drift from the last recorded values. Wrong is a stabilizer reading well below the last two visits with no drain, backwash or heavy rain to explain it: that is dilution, and it confirms the valve rather than the test kit. Where it appears, quantify it rather than repeating a dose that is about to be diluted again.
Reopen the fill stop, restore level, and verify the pump and the skimmer on the restored setting. Open the stop you closed in step 2 or step 3 only when the valve has passed step 5 or the plumber's correction is complete, and record the reopening next to the closing so nobody inherits a pool on a shut fill line. Accept when the level sits between one third and one half up the skimmer mouth, the pump primes and runs without air at the returns, and the skimmer weir floats and swings freely. Wrong is a pool left on a closed fill stop over a hot week, which is how a pump ends up running dry. Where the stop stays closed on purpose, that is a customer notification with a manual top-up instruction, not a silent decision.
Why the level is measured against the skimmer, not against the tile
Customers judge water level against the tile line because that is the visible edge, and it is the wrong reference. The tile band is a finish detail whose height varies with the build; the skimmer mouth is a hydraulic feature, and everything about the pool's circulation is designed around water sitting partway up it.
Below the bottom of the opening, the skimmer draws air and the pump loses prime, and a pump that runs dry cooks its mechanical seal in minutes rather than hours. Above the top of the opening, the weir door cannot swing, so surface debris floats past the skimmer instead of into it, and the pool looks dirty on a system that is running perfectly. That is the whole reason the acceptance in steps 1, 5 and 7 is written as a fraction of the skimmer opening: it is a range that both the pump and the skimming action can live in, and it reads the same for every technician on every pool.
The record this produces
The water record, attached to the property, because both the loss rate and the dilution signature are trends and neither is visible from one visit.
Fields: level on arrival as a fraction of the skimmer mouth, against the marked datum; bucket test start and end times, pool drop, bucket drop, and the net in inches per day and gallons per day; fill line isolated yes or no, with the times closed and reopened; the backflow finding described, air gap or assembly or neither, with a photograph; valve box condition and parts replaced; the shutoff proof result with the drip check; stabilizer, calcium hardness and total alkalinity with the previous two visits' values beside them; and the level, prime and weir check at departure.
The service manager reads the backflow finding first, because it is the only entry on this ticket that concerns drinking water. The shop lead reads the loss rate to decide whether the leak detection standard gets dispatched. The next technician reads the fill stop position, because a pool inherited on a closed stop is a dry pump.
Worked pass: a jumped water bill on a pool that always looks full
A 16 by 32 ft plaster pool, 512 sq ft of surface, roughly 20,000 gal, on a mechanical float autofill in a deck box, with an overflow line to the deck drain. Customer reports the water bill has roughly doubled. The pool level looks correct every week, which is exactly what the overflow line guarantees.
Step 1: level sits at about one third up the skimmer mouth, inside the acceptance, and a datum mark is made on the tile.
Step 2: fill stop closed 07:50 Monday, bucket set on the second step. Read 07:50 Wednesday. Pool down 0.44 in, bucket down 0.42 in over 48 hours, so 0.22 in per day pool against 0.21 in per day bucket. They agree within the rule's resolution, so the pool is not leaking and the loss is on the fill side.
Step 3 FAILS. The fill line is traced to a spout that terminates about 2 in below the water surface at the shallow-end wall, with no backflow assembly anywhere on the line and no air gap. The acceptance condition is an air gap above flood level or an approved assembly, and neither is present. Stop rule taken: the fill stop stays closed and tagged, the valve behind it is not serviced, the service manager is called from the deck, and the customer is told the same afternoon that this is a drinking water issue rather than a pool issue. A licensed plumber is referred and the water purveyor's cross-connection program is notified per the local requirement, with the spout photographed.
Steps 4 and 5 are deferred until the plumber's correction is done, and the ticket says deferred rather than passed.
Step 6 is run anyway, because it explains the bill. Stabilizer reads 28 ppm against 60 ppm recorded six weeks ago, with no drain, no backwash and no heavy rain in the log. Going from 60 to 28 means replacing 1 minus 28 over 60 of the volume, which is about 53 percent, and 53 percent of 20,000 gal is about 10,600 gal. Over 42 days that is 10,600 divided by 42, roughly 250 gal per day, which is under a fifth of a gallon a minute running continuously and would never show as a wrong level with an overflow to the deck drain. The valve is passing, and it is replaced rather than adjusted when the line is corrected.
Step 7: the fill stop is not reopened on this visit, and that is recorded explicitly with the reason and the time. The pool is topped up manually through a hose fitted with a hose bibb vacuum breaker to bring the level to mid-skimmer, the pump is confirmed primed with clear returns, and the weir is confirmed swinging. The customer is given a manual top-up instruction in writing until the plumber has been.
References
- The plumbing code your jurisdiction has adopted, in the edition adopted, for cross-connection control on a pool fill line, and the local water purveyor's cross-connection program for reporting and correction requirements.
- The autofill valve manufacturer's rebuild kit and instructions for the seat, diaphragm and travel adjustment the acceptance in step 5 reads against.
- The pump manufacturer's documentation on minimum suction level and dry-run damage, for why the level acceptance is written against the skimmer mouth.
- See related: the PoolService leak detection visit standard, the vinyl liner repair and replacement standard, and the partial drain and dilution decision standard.