If you've lived in the Treasure Valley for more than one summer, you've probably heard someone mention "pressure irrigation." If you're new here, you may have discovered it the hard way — a water bill that didn't match your sprinkler runtime, a neighbor's lawn looking suspiciously green on days yours isn't allowed to run, or a district notice in the mail you weren't sure how to read. Boise and the surrounding valley run on two separate water systems, and which one your lawn uses determines an entirely different set of rules.
Two systems, two sets of rules
Most Treasure Valley homes have access to treated city water from a municipal provider (City of Boise, City of Meridian, City of Nampa, etc.). That water goes through your meter, runs your indoor plumbing, and costs accordingly. It's available any time, at any volume, within your jurisdiction's water-use guidelines.
Pressure irrigation is different. It's a second system — usually connected to a separate outdoor meter or valve — that delivers raw, untreated canal water under pressure directly to your yard. The source is the Snake River drainage network: agricultural-grade surface water managed by irrigation districts that have served the Treasure Valley since the early 1900s. This water is not potable. It is significantly cheaper than city water for outdoor irrigation. And it comes with its own schedule, its own rules, and its own seasonal calendar that doesn't care about your lawn's needs in September — it cares about canal flows and infrastructure capacity.
The most important distinction: if your property has pressure irrigation access, you are almost certainly expected to use it for outdoor watering — and using city water for irrigation on a pressure-irrigation-served lot is something most districts and jurisdictions actively discourage, both for cost reasons and because it puts unnecessary load on the municipal treated-water system.
How the even/odd schedule actually works
The most visible rule in the Treasure Valley pressure irrigation world is the even/odd address schedule. Here's what it means:
Your irrigation day is determined by your property's street address number. Even-numbered addresses (2, 4, 6, 8... 1204, 1206) water on even-numbered calendar days. Odd-numbered addresses (1, 3, 5, 7... 1203, 1205) water on odd-numbered calendar days. The 31st of any month (an odd number) is a no-water day for both, giving the system a rest.
This isn't a soft recommendation. In most districts, it's an enforced operational limit. The pressure irrigation system is engineered and sized around the assumption that roughly half the connected properties are drawing water on any given day. When a neighborhood ignores the schedule and half the even-address lawns run on an odd day, pressure drops — sometimes dramatically. If you've ever noticed weak sprinkler coverage or heads that barely pop up during peak morning hours, you're often seeing the downstream effect of neighbors running off-schedule.
There's also a time-of-day component in many districts. Running irrigation in the early morning (4 AM to 9 AM) is standard practice and puts you in the lowest-demand window. Midday and evening running isn't prohibited, but pressure in some neighborhoods sags noticeably during peak-demand hours in July and August.
Settlers Irrigation District vs. other districts
Settlers Irrigation District is the largest residential pressure irrigation provider in the Treasure Valley, serving large portions of Boise, Eagle, Star, and surrounding areas. If you're in a planned subdivision in those areas, there's a good chance Settlers is your district. Their even/odd enforcement is real, and they communicate schedule violations through notices and, in some cases, service interruption.
But Settlers isn't the only player. Depending on exactly where you live, you might be served by:
- Nampa & Meridian Irrigation District (NMID) — covers much of Meridian, Nampa, Caldwell, and Kuna. Largest irrigation district in Idaho by acreage served.
- Middleton Irrigation District — serves the Middleton area west of Eagle.
- New York Irrigation District — parts of the Caldwell and Parma areas.
- City-managed systems — some municipalities (parts of Meridian, parts of Nampa) operate their own residential pressure irrigation infrastructure alongside or in place of district service.
Each district has its own schedule rules, its own water-delivery season start and end dates, and its own billing structure. The even/odd framework is nearly universal, but the enforcement culture, billing periods, and seasonal calendars vary. If you're not sure which district you're in, your property tax statement often lists irrigation district assessments as a line item — that name is your starting point. Your district's website or a call to their office will confirm your schedule and hookup details.
How to find your system and your day
Look outside before anything else. Pressure irrigation lots typically have a second shutoff valve or a small secondary meter box near the property line or curb — separate from your main city water meter. If you see two meter boxes, you almost certainly have pressure irrigation. If you only see one, you're likely on city water only for outdoor use (common in foothills neighborhoods, newer infill lots, and some rural-adjacent properties that predate district expansion).
Your district will have a map on their website that shows service boundaries. Settlers, NMID, and Middleton all maintain publicly accessible service-area maps. Enter your address, confirm which district covers your parcel, then look up their schedule page to confirm whether your even or odd assignment applies under any subdivision-level override (some large developments have a community irrigation controller that manages the even/odd internally, and you may be on a tighter window than the district default).
When pressure irrigation shuts off for fall — and what that means for your lawn
This is the part that catches people every year: pressure irrigation in the Treasure Valley runs on an agricultural calendar, not a lawn-care calendar. Most districts shut off delivery in October — Settlers typically ends delivery between mid-October and November 1, depending on canal conditions and the year's snowpack outlook. The exact date changes annually and is announced by the district, not set in stone.
For your lawn, this matters because the fall care sequence — aeration, overseeding, the final deep winterization watering — has to happen while pressure is still running, or you have to use city water for what's left. September is the actionable month. The window for overseeding, the last fertilizer application, and setting up your lawn for winter all close before the canal does.
It also means your sprinkler blowout timing is partially set by the district. You can blow out your system and winterize it any time after district pressure shuts off — but you should blowout before the first hard freeze (28°F or lower), which in the Treasure Valley typically arrives between mid-October and early November depending on your elevation and neighborhood. Foothills areas see hard freezes earlier than valley floor. Don't wait until the district shuts off to schedule your contractor, because everyone else is scheduling at the same time. Book in September while you still have lead time.
For the full blowout timing picture, the guide to sprinkler blowout timing in the Treasure Valley covers the freeze-date window, the foothills vs. valley floor difference, and why booking early matters more than people expect.
What happens if you ignore the schedule
Beyond the pressure-drop effect on your neighbors' systems, there are practical consequences for running off-schedule. In most districts, repeat violations result in a written notice, then a service shutoff. Getting pressure restored typically involves a fee and waiting for a district technician — not a same-day fix. In the middle of August, that's a problem.
There's also the mechanical reality: pressure irrigation systems — the shared mains, laterals, and control infrastructure — are sized for half the connected properties running on any given day. The schedule exists because the physics of the system require it, not just because districts want to restrict usage. When demand spikes above design load, pressure in the farthest reaches of the distribution network drops to the point where heads don't fully extend and coverage patterns fail. You water more, get less penetration, and your lawn suffers anyway.
September is when the two systems interact most
In early fall, Treasure Valley homeowners on pressure irrigation are managing two parallel concerns: using the remaining pressure irrigation season efficiently while planning for the city-water-only period after shutoff. The September lawn sequence (aerate, overseed, fertilize, step down irrigation) all runs on pressure irrigation for most people. The final winterization watering before blowout may end up on city water if pressure shuts off before you're ready.
Knowing which system you're on and when the season ends removes one variable from an already time-compressed fall window. If you haven't confirmed your district and your schedule, do it now — before September's calendar fills up.
For the full September sequence in one place, the September lawn checklist for the Treasure Valley walks through each step — aeration, overseeding, fertilizer, irrigation reduction, and blowout booking — with timing built in for both pressure and city-water users.
LawnWise is built specifically for the Treasure Valley — including pressure irrigation scheduling, district shutoff dates, and ET-based watering reminders that know which system you're on. Create your account and start today.