There are several ways to save water, and I'm sure you are aware of some: using drought-tolerant landscaping (i.e., replacing a grass lawn with other materials or plants that require less water), investing in low-flow shower heads and toilets and water-saving dishwashers and washing machines, being mindful of the number of laundry loads run per week--a full load of laundry is most efficient, soaking dishes in a dishpan to reduce the volume of water eventually required to rinse each dish, and so many more.

If we think about the high water use activity of washing clothes, the most effective ways to save water are to use a low-flow washer, run full loads, and buy concentrated detergent (this way, manufacturers save the water they would normally add to detergent).

As for materials which require less washing, the most stain- and odor-resistant materials are actually natural. Think hemp, linen, leather, bamboo, seaweed, and wool.

Wool is breathable and moisture-wicking, meaning when you sweat, instead of getting trapped inside the fabric, the sweat can evaporate from your skin into the air. Some materials are treated with essential oils like peppermint (which is antibacterial!) to keep them fresh for longer and reduce the number of washes they require. Synthetic fabrics can be designed to be moisture-wicking and hardy (meaning the clothes will last longer), but a big issue with synthetic fabrics is that they are not biodegradable and will remain on earth for thousands or even millions of years.

The most circumspect, sustainable solution to low-wash materials already exists -- look for cotton/bamboo blend or cotton/wool blend garments, and use peppermint and lavender oils to reduce the bacterial buildup that causes clothes to become smelly. Another easy way to reduce odor in clothes is to expose them to sunlight because the UV light can also eliminate bacteria (just be careful if you don't want the color of your clothes to fade!).