Planning Water Treatment for a New Build on the Palouse: What to Rough In Before the Drywall Goes Up

By Trent, owner of Palouse Water Pros · Moscow, Idaho · September 2026

If you're building a house around Moscow, Troy, Genesee, Deary, Princeton, or anywhere else in Latah County, the cheapest time to plan for water treatment is before the plumbing plan is final. I was a general contractor before I got into water treatment, and I did a lot of plumbing, so I know how this usually goes: the water gets tested after move-in, the equipment gets squeezed into whatever corner is left, and somebody ends up cutting drywall to run a drain. I like being brought in early. A little planning at the framing stage makes the install cleaner, cheaper, and easier to service for the life of the house.

This page walks through what to decide, when to decide it, and what to hand your builder and plumber so the rough-in is ready for whatever your water turns out to need.

Test the water before the plumbing plan is final

You can't design a treatment system around water you haven't tested. On a new well, that test should happen as soon as the well is drilled and the pump is running, not after the house is finished. Whether the water needs a softener alone, an iron and manganese stage, disinfection, or just a drinking-water system changes how much room you need, how many drain connections you need, and where things go.

Palouse wells commonly carry some mix of iron, manganese, and hardness, and some have coliform or tannin issues too. The Palouse well water guide explains why. A few practical notes for a brand-new well:

• Get the well driller's report. The driller files a Well Driller's Report with the Idaho Department of Water Resources, which records things like well depth, depth to water, and flow rate. Ask for a copy. The flow rate matters for sizing any equipment that backwashes.
• Let the well settle and flush. A freshly drilled well can run cloudy or carry disinfectant from the drilling process. Sample once it's been run and cleared, or the numbers won't represent the water you'll actually live with.
• Cover the health basics as well as the nuisance ones. The Idaho DEQ recommends testing private wells for bacteria and nitrate at least once a year. For a treatment design, I also want hardness, iron, manganese, and pH. If you're not sure what a lab report is telling you, see how to read a well water test.

Building in town? The same logic applies to city water. Hardness and chlorine taste are the usual questions there, and I've covered that on the Moscow city water page. Test the tap you'll actually be connected to before deciding.

The utility room: plan it like it matters

Treatment equipment needs a home. On most new builds that's a mechanical room, garage wall, or corner of the basement near where the water line enters. Whatever the location, it needs a few things:

• Floor space and height. A softener with a brine tank, plus possibly a filter tank or two, takes up real wall length. Leave room to lift a valve head off a tank and to carry salt bags in without climbing over anything.
• Clearance for service. Tanks shoved into a closet behind the water heater can't be serviced. I want to be able to reach every valve, bypass, and drain line without moving another appliance.
• A drain. Softeners and backwashing filters discharge water during regeneration. That water has to go somewhere: a floor drain, a standpipe, or a laundry sink close by.
• A 120V outlet. Most control valves plug into a standard receptacle. Put one right at the equipment location, not across the room behind the furnace.
• Heat. Palouse winters freeze unheated garages and crawlspaces. Treatment equipment and its drain lines need to stay above freezing.

Where the pressure tank sits

On a well system, the order is usually: well line in, pressure tank and pressure switch, then treatment, then the rest of the house. Treatment goes after the pressure tank so it sees steady, pressurized water. When I lay out a room, I want the pressure tank near where the line enters and a clear run of wall after it for the treatment train. If the pressure tank ends up on one side of the room and the only open wall is on the other, the piping gets messy fast.

The softener loop and keeping outdoor water untreated

The single most useful thing a plumber can do during rough-in is stub out a treatment loop: the main cold line comes into the utility room, goes out to an "in" and "out" connection where equipment will sit, and then continues to the house. Add a bypass so water keeps flowing while equipment is being installed or serviced.

Just as important: tee off the outdoor hose bibs and irrigation before the loop. There's no reason to soften water for the lawn, garden, or washing the truck. It wastes salt and puts unnecessary wear on the equipment. The one exception to think about: if your well has a lot of iron, untreated water on the sprinkler line can stain siding, concrete, and fences. That's a case-by-case call once the test is in.

More on softener sizing and setup is on the water softener page, and heavier iron and manganese has its own page.

Run a dedicated RO line during rough-in

If there's any chance you'll want a reverse osmosis drinking-water system, plan for it now. An RO unit can sit under the kitchen sink or in the basement or utility room below. Either way, the time to run a dedicated line to the kitchen faucet and to the refrigerator's water and ice connection is when the walls are open. Pulling a line through a finished wall later is where the cost and the patching come in.

RO systems also need a drain connection, and some newer units need an outlet under the sink. Ask for both. The reverse osmosis page covers how these systems work.

Drains and air gaps

Plumbing codes generally don't let a softener, filter, or RO drain line be hard-piped straight into the waste system. The discharge has to cross an air gap, an open break above the drain, so dirty water can never be siphoned back into the equipment. The exact height and how it has to be done vary, so check local code and your inspector's expectations rather than assuming. If the house is on septic, ask about where treatment discharge should go before the drains are set. Planning a drain spot in the right place during rough-in is simple. Adding one after the slab is poured is not.

Water heater considerations

Put treatment ahead of the water heater so it gets treated water. Hardness is what scales up heating elements and heat exchangers, and iron and manganese deposit in tanks. This matters even more with a tankless heater. Many tankless manufacturers list water quality limits for hardness in their installation manuals and don't cover scale damage under warranty, so read the manual for the model your builder picks. Planning for treatment at the same time as the heater keeps you inside those limits from day one.

When each decision happens

What to hand your plumber and builder

A short, written spec avoids most problems. Mine usually covers:

1. Equipment location, with the space it needs marked on the plan.
2. Treatment loop ("in" and "out" stubs) with a bypass, after the pressure tank.
3. Outdoor hose bibs and irrigation teed off before the loop.
4. A drain within reach of the equipment, with room for an air gap.
5. A 120V outlet at the equipment location.
6. Dedicated RO line to the kitchen sink and refrigerator, with a drain connection and outlet under the sink.
7. Water heater downstream of treatment.

Common mistakes I see on new builds

• No drain. The equipment spot has no floor drain or standpipe anywhere nearby, so the discharge line gets run a long way across the room.
• No outlet. An extension cord to a control valve is not a permanent solution.
• No room. The treatment gets tucked into a closet behind the water heater, where nobody can reach it to service it.
• Treatment planned after drywall. By then the loop, the RO line, and the drain all mean cutting into finished walls.
• Softening the outdoor lines. The hose bibs weren't separated, so salt gets spent on the lawn.

How it works

Call or text me as soon as the well is drilled, or earlier if you're still drawing plans. I'll come out, test the water on-site in front of you, and walk the plan or the site with you. You'll get a clear recommendation and a written proposal, including a rough-in spec you can hand straight to your builder and plumber. When the house is ready, I build and install the system myself with industry-standard, serviceable parts, then verify the treated water so you can see the numbers. I'll give you an honest timeline up front.

If you want to understand your water first, start with the Palouse well water guide or take the 2-minute water quiz. More on testing is on the water testing page, and common questions are in the FAQ.