A meta-efficient design for a bathroom.
Water in the bathroom: use filtered rain water, otherwise filter water very thoroughly (i.e. remove: chlorine, heavy metals, pesticides, pharmaceuticals, VOCs, radon, and other contaminants).
Channel greywater into a garden.
Purify the air using indoor plants.
Use radiant heat through the floor. Heat via direct sunlight. Otherwise: from direct, renewable source (i.e. wood or sunlight).
Heat water using a point-of-use instant water heater thus reducing water wait time and external tanks. Heat using a renewable source.
Contain shower heat by sealing entire shower (thus reducing the need to heat water). Use an ultra-low-flow, aerated showerhead. If the water is not filtered, remove chlorine using vitamin C. Heat water at point-of use, reclaim heat after use. Use non-slip surface reducing injuries (i.e. textured tile). Incorporate handles for accessibility. Make faucets reachable by children. Overall use open shower design.
Choose optimal towels.
Choose optimal soap but incorporate dispensers to converse.
See shower principles. For a tub, recommend an ofuro is recommended, specifically one made of Alaskan yellow or Port Orford white cedar: aromatic, repels bacteria. Or ceramic. Dead sea salt most optimal for bath.
A toilet that combines squatting, cleaning with water (bidet function), urine separation, feces composting (sewer-free). Use sewage to produce biogas (fuel). See my article: The Three Fundamental Flaws Of The Modern Western Toilet.
Natural where possible (suntubes, skylights, opaque glass windows) otherwise use meta-efficient lights. Use LED task lights (motion-sensing), and ambient lights (LED bulb preferred –see 75 watt LED equivalents). Also, use low-wattage LED motion-sensing lights for night-time trips (so as to not wake others).
Design for comfort and sufficient privacy.
Non-toxic, natural, waterproof, mildew-proof. Tile, naturally-treated wood, glass, stone.
If needed should be removable, washable.
Smooth, uncluttered surfaces to optimal cleaning.
Optimal cleaning products: non-toxic, organic. Scents: essential oils.