Water Softener Loop: Which Lines Should Get Soft Water?

Water Softener Loop: The Short Answer

A water softener loop is a pre-plumbed pair of pipes, usually in the garage or a utility area, where a softener connects to your home's water line. The lines your plumber ran through it are the ones that get soft water. Anything that branches off before that point stays hard.

For most homes with hard water, a sensible setup softens the lines that feed showers, sinks, laundry and the water heater, and leaves outdoor hose bibs and irrigation off the softener. Whether your kitchen cold tap should be soft is a personal call, and it mostly comes down to sodium. The Minnesota Department of Health (MDH) puts it simply: soften only what you need to.

What a Softener Loop Is (and What It Leaves Out)

Picture the water line coming into your house. In a home with a loop, that line is brought out to an accessible spot as a pair of pipes: one carries water to the softener, the other carries softened water back into the house. Until a softener goes in, the two ends are usually joined so water keeps flowing. When a softener is installed, it sits between them, and everything plumbed downstream of that pair gets softened water.

Here's the part people miss. A loop doesn't automatically mean "whole house." Lines can be branched off before the loop so they never see the softener. Outdoor hose bibs are often left off, and some homes also keep the cold tap at the kitchen sink on its own hard line. There's no single pattern; it depends on how your house was plumbed.

If your loop is outdoors, check your climate before you plan around it. A softener can go outside only where it never freezes, and even then it needs shade and protection from the weather. Freezing temperatures can crack the resin tank and damage the control valve, so an indoor spot that stays above freezing, such as a basement, utility room or heated garage, is the safer choice. If an outdoor spot is your only option, an insulated enclosure is essential. If you move the softener indoors instead, you're no longer using the outdoor loop, so the no-loop options below apply.

How to find out which lines your loop serves

Your builder's plumbing plans, or the plumber who did the rough-in, can tell you. If neither is handy, test once the softener is running. Hardness test strips make the difference easy to see: check the kitchen cold tap, a bathroom sink on cold, and an outdoor spigot. Any tap that still reads hard isn't on the softened side.

If you're building, ask during the plumbing stage. It's far simpler to change which lines a loop serves while the walls are still open than after the drywall goes up.

The Four Common Layouts, Compared

Most softener setups land on one of four patterns. None of them is wrong. Each one trades a little protection against salt use, sodium in your drinking water, or extra plumbing work.

Plenty of homes combine the last two: indoor lines soft, with the kitchen cold tap and outdoor lines left hard. That's close to MDH's own list, which goes a step further. It notes that people often choose to soften showers, sinks and laundry hookups, while toilets, hose bibs, basement sinks and other cold water taps typically don't need to be connected to a softener.

Is Softening Only the Hot Water Enough?

It can be. MDH notes that in many cases people choose to soften only the hot water. It's a reasonable choice when protecting the water heater is your main goal, since softening prevents mineral scale from building up inside pipes, fixtures and hot water heaters, according to the same fact sheet.

The catch is that almost every shower and faucet mixes hot and cold. With a hot-only setup, the cold share of that mix is still hard. You may still see some mineral spotting on glass and fixtures, and more soap film than with fully softened water, especially if your water is very hard. Toilets, the cold side of the washing machine and the cold side of the kitchen faucet stay hard too.

So hot-only is a real middle ground. Less water runs through the softener, and with a metered control valve, which tracks how much water it has treated, that means fewer regeneration cycles and less salt. A timer-based valve regenerates on its schedule either way. Whichever valve you have, a hot-only setup won't give you the full soft-water feel in the shower.

Should the Kitchen Cold Tap Get Soft Water?

This is the line most worth thinking through, and the reason is sodium. A softener that regenerates with salt trades the calcium and magnesium in your water for sodium. MDH says a softener that uses sodium chloride increases the amount of sodium in the water you drink at home.

For most people, that isn't a big deal. The EPA's 2003 drinking water advisory on sodium says drinking water doesn't play a significant role in sodium exposure for most individuals. The numbers matter more if someone at home is on a sodium-restricted diet. MDH also advises anyone with a history of high blood pressure to talk with a doctor about drinking softened water. EPA's guidance level of 20 mg/L was developed for people limited to 500 mg of sodium a day, and the advisory says it shouldn't be extrapolated to the whole population. Separately, to avoid taste problems, EPA recommends that sodium in drinking water not exceed 30 to 60 mg/L, a threshold set for taste-sensitive people. For how much sodium a softener actually adds, see our guide on whether softened water is safe to drink.

Three ways to handle drinking water

• Keep the kitchen cold tap hard. MDH suggests an unsoftened tap for cooking and drinking as one way to cut the sodium you drink. It's the simplest route when a loop is being plumbed for the first time.
• Soften everything and add reverse osmosis at the kitchen sink. University of Nebraska-Lincoln Extension lists sodium among the contaminants household reverse osmosis units remove, and notes that softening relatively hard water ahead of the membrane can extend its life. The whole house stays soft, and the water you drink carries less sodium. Crystal Quest® makes under-sink reverse osmosis systems for exactly this spot.
• Switch to potassium chloride. MDH notes you can regenerate with potassium chloride instead of sodium chloride to lower the sodium you drink. Our guide to choosing water softener salt compares the two.

Outdoor Faucets, Irrigation and Toilets

Outdoor water is the easiest line to leave off. Watering the lawn, washing the car and filling a pool don't need soft water, and if your softener has a metered control valve, every gallon that skips it is a gallon it doesn't have to regenerate for.

There's a plant-health reason too. Penn State Extension's guide to interpreting irrigation water tests notes that removing hardness with a sodium chloride softener often leads to elevated sodium, and that softening for irrigation should use potassium for regeneration rather than sodium to prevent damage from excess sodium. If your hose bibs run through the softener today, the bypass valve works as a short-term fix for a long watering session, though every indoor line gets hard water until you switch it back to service. Replumbing the outdoor lines ahead of the softener is the permanent one.

Toilets don't need soft water, so they're optional. If your loop already includes them, there's no reason to change it.

No Loop in Your House? Your Options

Plenty of homes were never set up with a loop. That doesn't rule out a softener. It just means the installer cuts into the main line instead of connecting to a ready-made pair of pipes. You've got three realistic paths.

1. Soften at the main line.

   The usual install puts the softener where water first enters the home, after the pressure tank on a well and before the water heater, so it treats hot and cold. The spot also needs a drain and, if the control valve is electric, a nearby outlet. Our step-by-step installation guide covers placement, the bypass valve and the drain connection.

2. Branch off the lines you want to keep hard.

   Hose bibs and the kitchen cold tap can be teed off the main line before the softener. This is where the extra work comes in, because the lines you keep hard need a separate supply run that branches off before the softener. If you're remodeling or the pipes are already exposed, that's the time to do it.

3. Soften only the water heater's supply.

   When running new lines isn't practical, putting the softener on the cold line that feeds the water heater gives you a hot-only setup without touching the rest of the plumbing. The same drain and power needs apply at that location.

What any of this costs depends on your plumbing, how far the main line is from a drain, and whether local code calls for a permit or a licensed plumber. Our water softener cost breakdown explains how a dedicated loop, a new drain line or a permit moves installation pricing.

Three Checks Before You Connect a Softener

Whichever layout you choose, these come straight from MDH's softening guidance and they're easy to overlook.

• Confirm you need one. MDH says a softener may be worth it when hardness is above 7 grains per gallon, or 120 mg/L. A test kit, an accredited lab or your water utility can tell you where you stand.
• Check whether your utility already softens. Water that's already softened by a community system doesn't need softening again, and MDH notes extra softening may cause corrosion problems in your home.
• Give new copper plumbing a head start. If your home has new copper plumbing, from a new build or a recent repipe, MDH recommends not running the softener for at least the first few weeks you use water there. That gives the plumbing time to form a protective mineral layer that lowers the risk of excess copper in your water.