Direct answer: A Watts softener with the W100 (WM100SM) valve regenerates in six steps: brine fill, backwash, brine draw, a second backwash, rinse and return to service. The factory setup in the manual is metered: gallons capacity on “AUTO,” regeneration at 2:00 a.m., and brine “prefill” two hours earlier, so fill starts at about midnight. To regenerate tonight, press and release REGEN; to regenerate now, hold REGEN for about 3 seconds. Salt use depends on the programmed capacity: the manual lists 6 lb of salt per cubic foot of resin for about 20,000 grains, 8 lb for 25,000 and 15 lb for 30,000.
Publisher boundary: Water System Guide is an independent research publisher, not a Watts dealer. This page uses the Watts water conditioner operating manual with the WM100SM valve (FORM 0500-200, PDF created 2006) and the Watts Water Quality dealer catalog C-WQ-Dealer 2604 (April 2026), reviewed October 15, 2026. It applies to Watts W100-valve softeners, including the current M3011, M3013 and M3015-CK10SM. Locksmith and twin systems use different controllers.
The regeneration steps
The manual lists the steps and their purpose (WM100SM manual, PDF page 5):
- Brine fill. “Brine tank is filled to dissolve salt for next regeneration.”
- Backwash. “Flow through the resin bed is reversed. Water flows upward expanding and agitating the resin bed.”
- Brine in. “Brine is educted from the brine tank and passes through the resin bed in a downward flow,” removing the calcium and magnesium on the resin, which is flushed to drain.
- Second backwash.
- Rinse. “The resin is now flushed downward at a set flow rate. This resettles the bed and rinses out any remaining brine.”
- Service. The softener returns to service.
The manual explains that “when the control valve is used as a down flow softener, two backwashes always occur.” It also says “the softener will adjust the backwash and rinse cycles automatically when the salt dosage is changed,” and that backwashes can be set to NORMAL or LONGER, which applies to all of them (WM100SM manual, PDF page 5).
Prefill: why the softener runs at midnight
With the prefill option, “the prefill starts two hours before the regeneration time set. During the 2-hour period in which the brine is being made, treated (softened) water is still available.” The manual’s example: with regeneration at 2:00 a.m., “fill occurs at 12:00 a.m., start of backwash cycle occurs at 2:00 a.m.” The quick-reference defaults list “Brine Refill . . . Pre” (WM100SM manual, PDF page 10).
What starts a regeneration
The valve “can be set to regenerate on demand (consumption of a predetermined amount of water) and/or as a time clock (passage of a particular number of days).” The quick-reference page lists the factory settings (WM100SM manual, PDF page 10):
| Setting | Default in the manual |
|---|---|
| Backwash duration | Normal |
| Gallons capacity | Auto |
| Brine refill | Pre (prefill) |
| Regenerant flow | dn (downflow) |
| Regeneration initiation | Normal + on 0 |
| Time of regeneration | 2:00 AM |
With gallons capacity on AUTO, the valve calculates capacity from the hardness setting and estimates the reserve “based on water usage.” The three regeneration-time options mean:
- NORMAL: regenerate at the preset time.
- on 0: regenerate “when the gallons capacity reaches zero.”
- NORMAL + on 0: regenerate at the preset time, unless capacity reaches zero first, in which case “regeneration will begin 10 minutes after no water usage.”
Installer settings that change the frequency
The installer menu opens by pressing NEXT and the up arrow together for 3 seconds (WM100SM manual, PDF page 11):
- Hardness: in grains per gallon, “default is 20 with value ranges from 1 to 150.” The manual notes the value “can be increased if soluble iron needs to be reduced.”
- Day Override: sets the maximum days between regenerations (1 to 28), or the fixed interval if gallon capacity is off. Set to “off,” regeneration “is based solely on gallons used.”
- Regeneration time: hour and minutes, default 2:00 a.m.
To convert a lab result to the hardness setting, the manual says to divide ppm by 17.1: “250 PPM divided by 17.1 PPM/gr. equals 14.6 gr.” Our Watts not-softening guide explains why the hardness setting matters when water turns hard.
Starting a manual regeneration
The manual gives two methods (WM100SM manual, PDF page 10):
- At the next regeneration time: press and release REGEN. “Regen today” flashes, and you can cancel by pressing REGEN again. This is “not allowed when the system is set to immediately regenerate when the capacity reaches zero.”
- Immediately: press and hold REGEN for about 3 seconds. “The user cannot cancel this request, except by resetting the control by pressing NEXT and REGEN buttons simultaneously for 3 seconds.”
The manual adds that “the control valve may be stepped through the various regeneration cycles by pressing the REGEN button” once a regeneration is running, and warns: “If brine tank does not contain salt, fill with salt and wait at least two hours before regenerating” (WM100SM manual, PDF page 12).
During regeneration the display shows the current step and time remaining. “If there is a demand for water when the system is regenerating, untreated water will be used,” so regenerate when nobody is running water.
Salt per regeneration
The manual’s exchange capacity data (WM100SM manual, PDF page 5):
| Salt per cubic foot of resin | Approximate capacity per cubic foot |
|---|---|
| 6 lb | 20,000 grains |
| 8 lb | 25,000 grains |
| 15 lb | 30,000 grains |
Its specification table gives the range for each W100SM model, as maximum and minimum capacity and salt (WM100SM manual, PDF page 4):
| Model (manual) | Resin | Capacity max / min | Salt per regen max / min |
|---|---|---|---|
| M3011-W100SM | 1 cu ft | 30K / 20K | 15 / 6 lb |
| M3013-W100SM | 1.5 cu ft | 45K / 30K | 22 / 9 lb |
| M3015-W100SM | 2 cu ft | 60K / 40K | 30 / 12 lb |
| M3017-W100SM | 3 cu ft | 90K / 60K | 45 / 18 lb |
The current catalog’s CK10SM models use the same resin volumes (1, 1.5 and 2 cubic feet) and maximum capacities (30,000, 45,000 and 60,000 grains), with a 350-lb salt fill in an 18 x 36 brine tank (dealer catalog, PDF page 20).
Our arithmetic: at the minimum setting, an M3013 makes about 30,000 grains from 9 lb of salt, or about 3,333 grains per pound. At the maximum, it makes 45,000 grains from 22 lb, about 2,045 grains per pound. The lower setting regenerates more often but uses salt more efficiently.
The manual recommends “a good grade of solar or pellet salt.” Its specifications list potassium chloride among compatible regenerants (WM100SM manual, PDF page 4).
Drain and backwash flow
Every backwash and rinse goes to drain, so the drain line matters. The manual says the drain line “should be a minimum of 1/2”,” and that “backwash flow rates in excess of 7 gpm or length in excess of 20’ require 3/4” drain line” (WM100SM manual, PDF page 3). The 2026 catalog lists backwash rates of 2.2, 2.7 and 3.5 gpm for the M3011, M3013 and M3015-CK10SM. The manual also says to “avoid overhead pipe runs to drain facility, as undue backpressure will affect the operation of injectors” (WM100SM manual, PDF page 6), which affects brine draw.
Sanitizing the system at start-up
The manual’s start-up instructions call for sanitizing: pour “about 3/4 to 1 1/2 ounce of 5.25% common household bleach into the brine well,” replace the cap and lid, then press and hold REGEN to start a regeneration immediately. It notes that this “can be done with or without salt in tank” and that “some water supplies may require periodic disinfecting” (WM100SM manual, PDF page 12).
When regeneration is not working
The manual’s system troubleshooting table lists these regeneration-related problems (WM100SM manual, PDF pages 24 and 25):
| Problem | Causes listed |
|---|---|
| Softener fails to regenerate | Power interrupted, defective timer, power failure |
| Softener fails to draw brine | Plugged drain line flow control, injector or injector screen; line pressure too low (raise to 20 psi); internal control leak |
| Excessive water in brine tank | Plugged drain line flow control or injector; foreign material in brine valve; defective controller |
| Unit used too much salt | Improper salt setting; excessive water in brine tank |
| Control cycles continuously | Broken or shorted switch |
If an “ERROR” code appears instead, see our Watts error codes guide. The Diagnostics menu (down and up arrows together) shows days and gallons since the last regeneration, daily gallon usage for the last 64 days, and regenerations since the last reset (WM100SM manual, PDF page 10).
Frequently asked questions
When does a Watts water softener regenerate?
The manual’s default is 2:00 a.m., with brine prefill starting two hours earlier. With gallons capacity on AUTO, it regenerates on the night capacity runs low, or when the Day Override interval is reached. With “on 0,” it can start 10 minutes after water use stops.
How do I force a Watts softener to regenerate?
Hold REGEN for about 3 seconds to start immediately. Press and release REGEN to schedule a regeneration for tonight. If the brine tank was empty, add salt and wait two hours first.
How much salt does a Watts softener use per regeneration?
It depends on model and setting. The WM100SM manual lists 6 to 15 lb for a 1-cubic-foot unit, 9 to 22 lb for 1.5 cubic feet and 12 to 30 lb for 2 cubic feet.
Can I use potassium chloride in a Watts softener?
The WM100SM manual lists potassium chloride among the regenerants the valve is compatible with. Its salt recommendation is a good grade of solar or pellet salt, so ask your dealer to adjust settings if you switch.