Greywater reuse in Costa Rica: what the rules actually allow

If you are building an eco-home in Nosara, a villa in the hills above Uvita or a small retreat on the Nicoya Peninsula, you have probably thought about it: why send perfectly good shower and laundry water into a tank when the garden is thirsty for half the year?

It is a fair question, and the honest answer has two parts. Costa Rican rules do not treat greywater as a separate, lightly regulated stream the way some US states do. They treat it as wastewater. But they do allow treated wastewater to be reused, with clear categories and limits. This guide explains both parts, so you can design something that works and stays legal.

It is general information based on the regulations in force in November 2026. Where the rules are not explicit about a situation, we say so.

What counts as greywater here

In everyday English, greywater is the water from showers, bathroom sinks, washing machines and sometimes kitchen sinks, everything except toilets. Costa Rican regulations don't use that split. They talk about ordinary wastewater (aguas residuales ordinarias), meaning all domestic wastewater: toilets, showers, hand basins, kitchen sinks, laundry and dishwashing. Greywater is simply part of it.

That matters, because every rule that applies to ordinary wastewater applies to your shower water too.

The rule for homes with a septic tank

Most homes outside city sewers use a septic tank and drain field, regulated by Decree 42075-S-MINAE, the regulation on disposing of treated wastewater into the ground. Two parts of that decree settle the greywater question for those homes:

• Annex 1, section D(a) makes it mandatory for all ordinary wastewater, listing toilets, showers, kitchen sinks, hand washing, laundry, dishes and similar uses, to go to the septic tank. Those flows must be included when the tank is sized.
• Article 34 bans disposing of untreated ordinary wastewater into the ground.

Dishwashing water must also pass through a two-chamber grease trap before the tank, cleaned every three months.

In plain terms: on a home served by a septic system, piping untreated greywater to banana circles, mulch basins or garden beds is not allowed. It is also one of the reasons inspectors find problems when a property is sold, because those lines are easy to spot.

There is a practical side, too. In the tropics, untreated greywater carries soap, grease, food particles and bacteria. In the dry season it can smell and attract insects; in the rainy season it can pool on saturated ground near the house.

Reuse is allowed after treatment

The legal path is to treat first, then reuse. Reuse of treated wastewater is governed by the Wastewater Discharge and Reuse Regulation, Decree 33601-MINAE-S. It applies to anyone who discharges or reuses wastewater and sets three key points:

1. Never for human consumption (article 27), in any case.
2. Eight reuse categories (article 28):

3. Quality limits for each category. For reused ordinary wastewater, the regulation measures flow, fecal coliforms and intestinal nematodes. The nematode limit is one egg per liter in every category, and fecal coliform limits range from 1,000 per 100 mL (types 1, 3 and 8) to 10,000 (types 2, 4 and 6).

Garden irrigation at a villa or hotel, where guests walk on the lawn, typically falls under Type 1. That is the strictest irrigation category, so the treatment has to be good enough to meet it consistently.

Approval and design of a reuse system

Reuse is not something you add later with a hose. The Regulation for Approval of Wastewater Treatment Systems, Decree 39887-S-MINAE, asks for:

• an irrigation design signed by a licensed professional, with a surface absorption test of the soil, the soil type, the crop or vegetation and the calculation report;
• plans of the irrigated area with one-meter contour lines and distances to property lines;
• at least two monitoring wells, one upslope and one downslope of the reuse area.

Treated water that is reused instead of discharged does not need a MINAE discharge permit (Decree 42128-MINAE-S, article 24), but the system does have to file operational reports with the Ministry of Health under Decree 33601, article 5.

What about a single house?

Decree 33601 exempts single-family homes from operational reports in the normal case. The regulations are less explicit about a single home that wants to reuse treated water, and we would not promise a simplified route that the rules don't describe. If you want reuse at a private home, have the approval and monitoring path confirmed with the Ministry of Health during design, not after construction.

Practical options that do work

For eco-homes, villas and small hotels, these are the options that fit Costa Rican rules:

• Reduce first. Low-flow fixtures and efficient appliances cut the volume your septic system has to handle, which also helps the drain field survive the rainy season.
• Rainwater harvesting. Roof water is not wastewater, so the reuse rules don't apply to it. Stored rainwater can cover much of a garden's needs in some regions and can supply toilets with proper plumbing. Keep it completely separate from the septic system.
• A well-designed septic system. For a home, a properly sized septic tank, or an improved septic tank with an upflow filter, plus a drain field calculated from a percolation test, is the standard solution. The treated water returns to the soil through the trenches. See our guide to septic systems in Costa Rica and our page on improved septic tanks.
• Composting toilets. Decree 42075 recognizes dry, composting toilets that separate urine and feces, with at least two concrete chambers and setbacks, as a substitute for latrines and septic tanks where no working sewer is available. The rest of the household's wastewater still has to be treated properly.
• A small treatment plant with reuse. For a boutique hotel, a retreat or a group of villas, a wastewater treatment plant can produce water clean enough for Type 1 irrigation. In Guanacaste, where it barely rains from December to March, that can make a real difference. Our guide for boutique hotels covers it in more detail.

Plan for the rainy months

Reuse has a seasonal problem: when it rains, nobody irrigates. From May to November, especially in September and October, soils are saturated and irrigation is pointless or harmful. Decree 39887 allows combined disposal: reuse in the dry season and, the rest of the year, infiltration, discharge with a permit or another approved route. That backup has to be designed from the start. Our guide to the rainy season and septic systems in Guanacaste explains why.

Common mistakes

• Running laundry water to a separate pit or trench. Article 33 of Decree 42075 bans absorption pits for any wastewater, treated or not.
• Diluting effluent with rainwater or well water to make it look cleaner, which article 32 forbids.
• Installing an off-the-shelf greywater kit designed for another country's rules, without a Costa Rican design or approval.
• Forgetting that a future buyer's inspector, or the Ministry of Health after a neighbor's complaint, will look at where every pipe goes.

How we can help

At Ingeniería de las Aguas we design septic systems, improved septic tanks and treatment plants, including reuse for irrigation, and we handle the permits with the Ministry of Health and other agencies. If you are planning an eco-home or a small hospitality project and want to reuse water legally, send us the location, the number of bedrooms or rooms and your idea on WhatsApp, or use our contact page. We will tell you which option fits your site and what the approval involves.