Building in Los Osos: Sewer, Water, Growth Allocations, Habitat Plan Coverage and Permits

Planning guide · updated October 2026

Los Osos asks more of a building project than almost any other town in San Luis Obispo County. For many years new homes were largely on hold while the community waited on a sewer and a plan for its groundwater. The sewer went into operation in 2016, and the County now has a habitat plan and a yearly growth allocation system that open a path to build again, but each piece has its own paperwork, timing and limits. This guide walks through what a new home, remodel or addition in Los Osos and Baywood Park needs: sewer or septic, water, growth allocations, habitat plan coverage, coastal permits and the site itself, and the order we line them up in.

Harrod Built builds custom homes, remodels, additions and ADUs on the Central Coast, including in Los Osos, Baywood Park, Morro Bay and Cayucos. To talk through a vacant lot, a remodel or an addition in Los Osos, call 805-712-8993 or send the form at the end of this page.

The short answer

For a new home on a vacant lot in Los Osos, plan on five things before the building permit: water and sewer will-serve letters, a Title 19 water conservation certificate, a growth rate allocation from the County’s yearly limit, coverage under the Los Osos Habitat Conservation Plan with reserved mitigation credits, and usually a coastal development permit. Allocations and credits are released on a calendar, and as of September 2026 the County said all of its 2026 habitat credits were reserved, with more expected in early 2027. Remodels and additions skip the allocation but still need habitat coverage for new ground disturbance and often a coastal permit. Call 805-712-8993.

1. Why Los Osos is different

Sewer, water and habitat, all at once

Three issues shape every project here. The town sits on a single groundwater basin that supplies all of its drinking water and is watched closely for seawater intrusion. Much of the town was long served by septic systems in sandy soil over that basin, which led state water regulators to restrict new discharges and, in time, to the community sewer. And most of the urban area sits on the Baywood fine sands, home to protected species found almost nowhere else. The County’s Los Osos page pulls the requirements together, citing the 2024 Los Osos Community Plan.

A planning summary drawn from the County’s Los Osos pages, read October 25, 2026. Each lot has its own mix, and the County updates these programs often (we confirm per lot).

Our Los Osos page gives a short overview of building here. This guide goes step by step, because in Los Osos the order matters as much as the steps themselves.

3. Water

The basin, the water companies and the retrofit rules

All of Los Osos’ drinking water comes from the Los Osos Groundwater Basin. The basin is managed under a court judgment by the Los Osos Basin Management Committee, made up of the three water companies and the County, which publishes yearly monitoring reports and a sustainable yield estimate. Those findings feed into how much new building the County allows each year.

Will-serve letters

Three water companies serve the town: the Los Osos Community Services District, Golden State Water Company and S&T Mutual Water Company. The County’s Development Request Form asks which one serves the lot and whether a water will-serve letter is in hand, and a sewer will-serve letter too where the lot is on the sewer. Each company has its own process; the Community Services District, for example, has adopted a yearly review of water supply before accepting applications for new service (we confirm per lot).

Retrofit-to-Build (Title 19)

Under the County’s Title 19 Retrofit-to-Build handout, new development that uses basin water has to retrofit older plumbing fixtures in existing homes and businesses to save twice the water the new development is expected to use. Savings come from replacing toilets, showerheads and clothes washers, or adding a demand-initiated hot water recirculation system, and they must happen within the same water company’s service area as the new home. The County then issues a water conservation certificate, which is needed before the building permit is issued. The savings tables are updated every five years, so we check the current version on each job.

Retrofit-on-Sale (Title 8)

Separately, Title 8 requires retrofit verification for homes in the basin before they are sold. If you are buying a Los Osos house to remodel, ask whether that verification was completed, and plan new fixtures that meet the current efficiency limits.

5. The Los Osos Habitat Conservation Plan

Coverage for any new ground disturbance

In February 2024 the U.S. Fish and Wildlife Service Ventura office approved the County’s Los Osos Habitat Conservation Plan (LOHCP) and issued a community-wide incidental take permit, valid for 25 years. It covers four species: the Morro shoulderband snail, the Morro Bay kangaroo rat, Morro manzanita and Indian Knob mountainbalm. Instead of every owner negotiating with the wildlife agencies alone, projects join the County’s permit through a Certificate of Inclusion.

The County’s Los Osos Habitat Conservation Plan page lays out the steps:

1. Development Request Form. Submitted by email with a site disturbance plan (permanent disturbance such as the house, decks, hardscape and driveway, plus temporary disturbance such as grading, trenching, landscaping and staging), a biological visual survey for the covered species by a County-listed biologist no more than a year old, construction plans, and water and sewer will-serve or continue-to-serve letters.
2. Credit Reservation Form. If credits are available, the County reserves habitat mitigation credits for that project and lists the avoidance and minimization measures that apply. In most cases one credit covers one square foot of ground disturbance, so a compact footprint and a tight staging plan matter.
3. Building permit. For projects that need only a building permit, the application must be submitted within 45 days of the reservation and be ready to issue within a year, or the credits return to the pool.
4. Certificate of Inclusion. Issued with the building permit once the conditions are met. It is a binding agreement, and the construction measures in it must be followed on site.

Credits come from County habitat restoration and conservation projects, and the plan only allows the County to hand out credits it has already earned. Credits are split among categories each January and pooled for anyone on October 1. As of September 17, 2026, the County said all credits available in 2026 had been reserved, that it would not accept more credit applications in 2026, and that more were expected in early 2027. That makes the habitat step the most timing-sensitive part of a Los Osos project right now (we confirm per lot).

The County’s Los Osos town hall FAQ adds that additions and redevelopment projects causing temporary or permanent ground disturbance also need a Certificate of Inclusion, that parcels in mapped habitat for the kangaroo rat or the snail are treated as environmentally sensitive habitat and need a biological resource assessment, and that limited development in the Priority Conservation Area requires setting aside habitat on site.

Morro manzanita

On August 13, 2026, the California Fish and Game Commission listed Morro manzanita as threatened under the California Endangered Species Act. The County is pursuing a state permit to cover it. Until then, if a biologist finds Morro manzanita on a lot, the County says the project must avoid and minimize impacts and work with the California Department of Fish and Wildlife on its requirements, and projects needing a discretionary land use permit must get state take coverage before environmental review concludes (we confirm per lot).

7. The site itself

Sand, wind, salt air and fire

• Sandy soils. The dune sands drain fast and move easily. A soils report guides the foundation, and grading, drainage and erosion control are planned to keep sand on the lot and water soaking in where the County allows.
• Wind and salt air. Onshore wind and fog off the bay call for corrosion-resistant fasteners, connectors and flashing, and windows, siding and decking chosen to hold up near the water.
• Fire zones. If the lot is mapped in a fire hazard severity zone, the house follows the wildfire-resistant construction rules of Chapter 7A. The County Fire Department’s fire hazard severity zone information links the state maps; our guide to building in a fire hazard severity zone covers the materials, and our rebuild guide covers rebuilding.
• Energy code. Permit applications filed on or after January 1, 2026 follow the 2025 Energy Code; our Title 24 overview explains the basics.
• Landscape. Because landscaping and fire clearing count as ground disturbance under the habitat plan, the yard is planned with the house, not after it.

9. The order of steps

How we line up a new home in Los Osos

The steps overlap, and several have deadlines that start running once the next one is reached. This is the order we plan them in:

The order we plan a new home on a vacant Los Osos lot. Remodels and additions skip some steps; projects with a land use permit add others.

For a shorter overview, see our page on building in Los Osos. For the permit path across the County, see our SLO County permits guide; if you are still choosing a lot, our guide to buying land to build on covers what to check. If you are weighing managing the work yourself, read our owner-builder vs licensed contractor guide, and before hiring anyone, see how to check a CSLB license and the Contractors State License Board’s guidance on hiring a licensed contractor.

How we help

Building in Los Osos with Harrod Built

• Lot first. Harrod Built is a family general contractor based in Paso Robles, CSLB #986950. We walk the lot or house with you, check the sewer, water, allocation, habitat and coastal steps with the County, and give a written estimate. You can confirm our license on the state license lookup.
• The right consultants, in the right order. Biologists, surveyors, soils engineers and designers, scheduled so the survey, the disturbance plan and the reservation deadlines line up.
• Small footprints, well detailed. Plans that keep ground disturbance tight, and construction details for sand, wind and salt air.
• Design support. Harrod Drafting & Design, our drafting studio, draws homes, additions and permit sets, and we also build from plans by outside architects.
• Outside the house. Paso Robles Landscaping can plan the yard around the habitat measures, with drainage and water-efficient planting.

We build custom homes, home additions and remodels in Los Osos, Morro Bay, Cayucos, Cambria and San Luis Obispo, and across San Luis Obispo, Monterey and Santa Barbara counties, with general contracting and design-build; our process page explains how a job runs. Our nearest finished home is the Contemporary home in Morro Bay.

Thinking about building or remodeling in Los Osos? We can look at the lot or house with you, sort out which of these steps apply, and give you a written estimate. Call 805-712-8993 or contact us.

Sources: County of San Luis Obispo Planning & Building: Los Osos page (updated September 17, 2026), Los Osos Habitat Conservation Plan implementation page, residential growth rate allocation page, letters to waitlist property owners, Los Osos Development Request Form, Los Osos community development town hall FAQ, Los Osos Groundwater Basin page, Title 19 Los Osos Groundwater Basin Retrofit-to-Build handout (LNG-1016), and the PermitSLO how-to guides. County Public Works: Los Osos Wastewater System page, boundary map and rules and regulations (County Code Chapter 8.93). Los Osos Basin Management Committee; Los Osos Community Services District. California Department of Fish and Wildlife (California Endangered Species Act); U.S. Fish and Wildlife Service Ventura office; California Coastal Commission. California Energy Commission 2025 Building Energy Efficiency Standards. San Luis Obispo County Fire / CAL FIRE fire hazard severity zone information. Contractors State License Board guidance on hiring a contractor. All checked October 25, 2026. This guide is general information, not legal, biological or code advice; County Planning & Building, the water companies and the wildlife agencies have the final word on a given lot.