Using 3D printed objects with water, especially for drinking or food storage, is generally not recommended without specific precautions and material certifications, as many common 3D printing materials are not inherently water-safe or food-safe.
While a 3D printed object might appear solid, its suitability for water contact, particularly for human consumption, involves several critical considerations, including material degradation, potential chemical leaching, and the inherent porosity of prints.
Understanding "Water Safe" in 3D Printing
The term "water safe" can be interpreted in a few ways when it comes to 3D printing:
- Material Integrity: Will the 3D printed object degrade or break down when exposed to water?
- Chemical Safety: Will the material leach harmful chemicals into the water it contacts?
- Hygienic Safety: Can the object be easily cleaned and kept free from bacteria or mold growth when in contact with water?
Most standard 3D printing materials and processes present challenges for all three aspects.
Material Degradation and Rust Concerns
Many common 3D printing plastics, such as PLA (Polylactic Acid), are biodegradable. While this is an environmental benefit, it means they can degrade when exposed to water over extended periods. This degradation can weaken the object and potentially release microparticles or chemicals into the water.
When it comes to metal 3D prints, direct contact with water can lead to different issues. Metals generally develop rust due to oxidation by water, which can compromise the structural integrity and introduce contaminants.
Chemical Leaching and Porosity
Beyond degradation, the safety of 3D printed objects with water is primarily compromised by:
- Chemical Additives: Most filaments contain various additives, dyes, and plasticizers that are not tested or certified for food or drink contact. These chemicals can leach into water, especially over time or with temperature changes, potentially posing health risks.
- Print Porosity: FDM (Fused Deposition Modeling) 3D prints, made by layering extruded plastic, are inherently porous. Even with high infill and thick walls, microscopic gaps exist between layers. These tiny crevices can harbor bacteria, mold, and other microorganisms, making thorough cleaning difficult or impossible and creating unsanitary conditions, particularly for drinking water.
- Resin Prints: Objects printed with resins (SLA, DLP, MSLA technologies) often require post-curing and cleaning with chemicals like isopropyl alcohol. Residual uncured resin or cleaning agents can be highly toxic and should never come into contact with consumables.
Water Resistance vs. Food Safety
It's crucial to distinguish between a material being water resistant and food safe.
- Water Resistance: This refers to a material's ability to resist the ingress of water or withstand water exposure without degradation. Materials with good water resistance are often classified using the Ingress Protection (IP) Code, such as IP 67 and/or IP 68. An IP67 rating means the item is protected from immersion in water up to 1 meter for 30 minutes, while IP68 offers protection for continuous immersion under specified conditions. While these ratings indicate durability in water, they do not imply that the material is safe for food or drink contact.
- Food Safety: This refers to a material's suitability for contact with food or beverages without causing harm to consumers. This usually requires specific certifications from regulatory bodies like the FDA (Food and Drug Administration) in the US or EFSA (European Food Safety Authority) in Europe. Most off-the-shelf 3D printing filaments lack these certifications.
Factors to Consider for Water Contact
When contemplating using 3D printed items with water, consider these aspects:
| Aspect | Explanation |
|---|---|
| Material Type | PLA: Generally not suitable for long-term water contact due to degradation and porosity. ABS: Better water resistance than PLA but often contains more questionable additives; also porous. PETG: Often considered a "safer" choice for water contact due to its non-toxic nature and good chemical resistance, but still porous and rarely food-grade certified. Nylon: Can absorb water (hygroscopic) leading to dimensional changes and potentially microbial growth. Resins: Generally not suitable due to toxicity of uncured resin and post-processing chemicals. Specialty Food-Safe Filaments: A few manufacturers offer truly food-safe filaments, but they are rare and require strict adherence to food-safe printing practices. |
| Print Quality | Layer Adhesion: Poor layer adhesion can increase porosity, making the object more susceptible to water ingress and bacterial growth. Infill: Lower infill rates mean more internal voids, creating more surfaces for water and contaminants to reside. |
| Post-Processing | Coatings/Sealants: Applying food-safe epoxy, sealant, or glazes can mitigate porosity and create a barrier between the 3D printed material and water. This is often the most practical solution for making a print "water-safe" for limited use, but finding truly food-safe and durable coatings can be a challenge. |
| Intended Use | Short-term vs. Long-term: A 3D printed vase for decorative purposes (non-drinking water) might be acceptable, whereas a cup for daily drinking is not. Temperature: Hot water can accelerate chemical leaching and material degradation. |
Examples and Practical Insights:
- Vases/Planters: For decorative uses with non-potable water, coating the interior with a waterproof sealant (e.g., epoxy resin or clear silicone) is highly recommended to prevent leaks and degradation of the print material.
- Hydroponic Systems: For elements that don't directly contact edible parts of plants, materials like ABS or PETG might be used, but ensuring no harmful chemicals leach into the water that feeds the plants is crucial.
- Water Bottles/Cups: Avoid entirely unless using a certified food-grade material AND an internal food-safe liner/coating, AND the entire process is certified food-safe. The risk of bacterial growth in porous layers is significant, even with "food-safe" plastics.
- Aquarium Decor: Ensure any materials used are inert, non-toxic to aquatic life, and fully cured/sealed. Many 3D printing materials are not suitable due to potential chemical leaching.
Solutions for Safer Water Contact
If using 3D printed objects with water is unavoidable, consider these approaches:
- Choose Certified Materials: Seek out filaments specifically marketed and certified as "food-safe" or "medical-grade." However, remember that certification applies to the raw material, not necessarily the printed object, as the printing process itself can introduce contaminants or porosity.
- Apply Food-Safe Coatings: For objects intended for short-term, non-ingestion-critical water contact, apply a food-grade epoxy resin or similar sealant to create a smooth, non-porous, and chemically inert barrier. Ensure the coating itself is FDA-approved for direct and indirect food contact.
- Design for Cleanability: If possible, design objects with smooth, simple geometries that are easy to clean and sanitize. Avoid intricate internal structures.
- Regular Replacement: For critical applications, regular replacement of 3D printed components can help mitigate issues of degradation and bacterial buildup.
In conclusion, while 3D printed objects can be made water-resistant with certain materials and post-processing, making them truly water-safe for drinking or long-term storage, especially concerning human health, is a complex challenge requiring careful material selection, specific processing, and often, regulatory certification. For most consumer applications, it is safest to assume that standard 3D prints are not suitable for direct, prolonged contact with drinking water.
