Have a strip wash…you, know that thing you did as a kid and hated? Boil a kettle or pan of lake or river water and mix with cold water to your desired temperature, strip off and wash the essential pits and bits at the sink or from a bucket. Hard to manage without privacy unless you’re a complete exhibitionist…there are some places in the world where that’s not ok and you will be arrested for getting your kit off. If you’re in one of those places, use a shower tent and if that’s too much to cart around, wear your swimmers and get clever with your towel.
Always use biodegradable soap and dispose of your used water responsibly i.e. at least 20m from a water course.