How to Install a Water Softener Yourself

This guide is built from two manufacturer installation manuals: A.O. Smith's cabinet softener manual (models 350C, 400T and 450T) and Morton's System Saver manual (M20 to M34), plus a state plumbing code example. Your own softener's manual always comes first, because valves, fittings and programming differ by brand.

Can You Install It Yourself?

Usually, yes. Store-brand softeners are designed for homeowner installation. A.O. Smith's manual recommends "basic plumbing knowledge" and suggests a professional if you need to cut pipe, drill or connect into existing plumbing. The real question is how comfortable you are cutting into your main water line. If your plumbing is copper, PEX or CPVC and you have done a faucet or water heater swap before, this is a reasonable DIY project.

Two cases where you should call a plumber: if local code requires one (Morton's manual notes Massachusetts code 248-CMR requires a licensed plumber), and if there is no drain within reach of the main line, which may mean new drain plumbing. Some towns also require a permit, so check with your building department before you start. For typical professional installation costs, see our water softener cost guide.

Before You Start: Checklist

The A.O. Smith manual lists these conditions to confirm before installing:

Morton's manual adds a minimum inlet flow of 3 gallons per minute and a 125 psi maximum, and warns that if daytime pressure is over 80 psi, nighttime pressure may go higher. A cheap hose-bib pressure gauge screwed onto an outdoor faucet tells you where you stand. Test hardness with hardness test strips or one of the kits in our test kit guide. If your water has sand, sulfur, bacteria, tannins or high iron, both manuals say to treat that before the softener; see well water filtration.

Tools and Parts

A.O. Smith lists a basic toolkit: adjustable wrench, pliers, screwdriver, hose clamp and fittings to connect its 1 inch valve to your pipe. In practice you will usually also want:

• Pipe cutter for your pipe type (copper tubing cutter, PEX cutter or PVC cutter)
• Connection fittings to go from your pipe to the softener's ports: a softener installation kit, push-to-connect fittings, or PEX or copper adapters
• Drain tubing: 1/2 inch I.D. drain tubing if not supplied, plus extra for the overflow line
• An air gap fitting if you are draining into a standpipe
• A ground clamp and #4 copper jumper wire if you are cutting metal pipe
• PTFE (thread) tape, a bucket, towels and a flashlight
• Softener salt: A.O. Smith recommends pellet, cube or solar salt, not rock salt. Softener salt pellets are the common choice.

Choosing the Location

The manuals agree on the basic layout:

• After the main shutoff and well pressure tank, and after any sediment filter or water meter.
• Before the water heater. A.O. Smith recommends at least 8 to 10 feet of pipe between the softener outlet and the water heater inlet. If you have less than 10 feet, it says to fit a check valve close to the water heater (an expansion tank may also be used), and to make sure the heater has a properly rated temperature and pressure relief valve.
• Leave outdoor faucets on hard water. Morton notes this avoids wasting salt and soft water on lawns.
• Near a drain and a non-switched outlet.
• Somewhere that never freezes, out of direct sun, with room to reach the plumbing behind it. Morton says freeze and hot water damage void its warranty. A.O. Smith says a unit installed outdoors must be covered.
• Carbon filters go after the softener on well water, unless the filter maker says otherwise (A.O. Smith).

Step-by-Step Installation

1. Shut off the water heater. Turn off the power, or set a gas heater to "Pilot." Do not drain the water heater; Morton warns this can damage the elements.
2. Shut off the main water supply and open faucets (hot and cold) to depressurize and drain the lines.
3. Inspect the inlet pipe. A.O. Smith says to clean or replace pipe plugged with lime or iron.
4. Set the softener in place and attach the bypass valve. Check the flow arrows on the bypass: A.O. Smith's manual specifically warns against installing a softener backward.
5. Cut the main line and connect inlet and outlet. The A.O. Smith valve has 1 inch male NPT connections and works with copper, PEX or CPVC. Morton lists copper, threaded pipe, PEX, CPVC and other potable-approved pipe. Never solder near the plastic valve or adapters. Both manuals say torch heat will damage them, so sweat copper fittings before attaching them.
6. Restore the ground. If your house uses the metal cold water pipe as an electrical ground, a plastic bypass breaks that path. Morton says to clamp a #4 copper wire across the cut section; A.O. Smith calls for two grounding clamps and #4 copper wire on metallic plumbing and warns that skipping it can cause electric shock. Check local electrical code.
7. Connect the drain line and the overflow line as described in the next section.
8. Flush and check for leaks. With the softener in bypass, turn the main supply back on and run a cold faucet to clear flux, air and debris. Then shift the bypass slowly to service so the tank fills gradually, purge air from a cold faucet, and check every connection. Fix leaks with the water off.
9. Plug in the transformer to a non-switched outlet.
10. Add water and salt, sanitize and program (see Startup below).
11. Restart the water heater.

Drain Line and Air Gap Rules

The drain is where most DIY installs go wrong. During regeneration the softener sends backwash and brine water out under pressure. The drain hose must not be connected directly into a drain pipe. Instead it must end above the drain with an open air gap, so sewer water can never be siphoned back into your drinking water.

Local code can be stricter than either manual. Illinois's plumbing code, for example, requires softener drain lines to discharge through a vertical air gap at least twice the pipe diameter and never less than 2 inches, and requires a double check valve backflow preventer on the supply line for many softener types (Illinois Section 890.760). Check what your state or town has adopted.

Overflow line: cabinet softeners also have a gravity overflow fitting on the brine tank that drains away water if the tank overfills. A.O. Smith requires 1/2 inch I.D. tubing from this fitting to a drain at least 3 inches lower, with a 2 inch air gap, never run overhead. A.O. Smith's rule: do not join the drain and overflow lines together.

Startup: Salt, Sanitizing and Programming

1. Add water and salt. Morton's manual says to add about 3 gallons of clean water to the salt tank, then salt. A.O. Smith also has you add water at startup and notes this is the only time you add water by hand; after that, keep the salt level above the water level.
2. Sanitize. Morton suggests pouring about 3 oz (6 tablespoons) of household bleach into the brinewell, starting a manual recharge, and then running a cold faucet for about 50 gallons (at least 20 minutes). A.O. Smith gives 4 fluid ounces of 5.25% bleach in the brine well, followed by a manual regeneration. Do not mix bleach with resin cleaner.
3. Program it. Set the time of day, your compensated hardness and the regeneration time. A.O. Smith suggests regenerating when water is not in use (the classic is 2:00 AM). If you have more than one water treatment appliance, it recommends 2 hours between their regenerations.
4. Get soft hot water. Your water heater is full of hard water and will turn over in a few days. Morton says that for soft hot water right away, wait until the first regeneration is over, then drain the water heater until it runs cold.
5. Test. After a day, check a cold faucet with test strips. It should read close to zero.

Keep the salt level at least one-third full (A.O. Smith) and do not mix salt types. For ongoing salt and running costs, see the cost guide.

Common Mistakes

• Installing it backward. Check the inlet and outlet arrows before you connect anything.
• Pushing the drain hose into the drain pipe instead of leaving an air gap.
• Reducing the drain or overflow tubing size, or joining the two lines together.
• Soldering near the valve. Heat damages the plastic.
• Forgetting the ground jumper on metal pipe.
• Plugging into a switched outlet, so the clock resets and regenerations are missed.
• Leaving the bypass in bypass after flushing, so untreated water keeps flowing.
• Skipping the pressure check on high-pressure homes or wells.
• Choosing a spot that freezes.

Still choosing a unit? Compare Whirlpool, Rheem, Morton and A.O. Smith, read our Fleck 5600SXT review, or see best water softeners. If something goes wrong after installation, try our troubleshooting guide.

Frequently Asked Questions

Last updated: October 2026. Sources: A.O. Smith softener owner's manual, Morton System Saver installation manual, Illinois Plumbing Code Section 890.760.