Increasing your guinea pigs urine volume is important to prevent urinary health problems like sludge build up or urinary track infections.
What most people do (as recommended by most vets) to get more water into a guinea pig is to feed more wet foods… especially greens. It is true that when guinea pigs eat these foods that they are consuming a lot of water (most greens are about 90% water). However most people don’t realize that when guinea pigs eat greens that they reduce how much water they drink… and they eat less hay too!
Encouraging your guinea pigs to eat more dry hay will greatly increase the amount of water they drink! In fact it will increase their urine volume (by 300% to 400%) more than feeding them wet foods (like salads, greens, and veggies) which decrease the amount of hay they eat and water they drink.