Maurten drinks are not like Skratch or other powdered sports drink where you could adjust the ratio of the powder to water for flavor. While you should always follow the recommended amount of water, this is crucially important with Maurten. If there is too much water Maurten's hydrogel technology won't form properly and you will end up with too many carbs in your stomach and stomach distress.
Mix Maurten Drink Mix 160 and Maurten Drink Mix 320 will exactly 500ml/17 oz of water. Do not add in more water and remember that most water bottles these days are 21 oz, so if you mix 21 oz of water with 1 packet you will not be happy. If you have to guess, air on the side of too little (i.e. 400ml of water).
Another unique characteristic is not using water that has a high mineral content when mixing Maurten. Avoid water that has more than 40mg of Calcium per Liter. While I'm not sure how I would measure that, the safe bet is to use tap water which will almost always have a low mineral count. If you are using bottled water, it should say on the label the calcium content.
I'm often trying to mix Maurten into larger 24 oz water bottles or a 2-liter hydration pack. What I do is get a large 1.5L drinking container and put in 3 Maurten Packets and mix in 1.5L of water. This way you get the ratio correct, stir it and let it sit for a few minutes. Then I pour it into my larger 24 oz bottles and it works like a charm.
Another pro tip from the EF Education First Tour de France Team is mixing Maurten Drink Mix 160 and a Maurten Drink Mix 320 together to get a hybrid dosage that is 60g of Carbs and 240 Calories. Do this by mixing 1 packet of each in 1L of water.
A common question we get is when to mix your Maurten. You can mix your Maurten the night before and it will be good to go the next day. I would avoid freezing it and generally prefer to leave it at room temperature and not in the fridge.