North Marin Water District approved a rate hike on Tuesday, effective July 1, which will increase yearly water bills by about five percent, or $31 for the typical customer. The district says it needs to raise prices to help fund a $1.25 million project to make its West Marin water treatment plant more efficient. The sand filtration system, which removes iron and manganese from the district’s ground water that comes from Lagunitas Creek, must be…