Refreshing cucumber and pear juice

Name: Refreshing cucumber and pear juice
Prep time: 5 min
Cook time: 25 min
Total time: 30 min
Cuisine: European, British
Ingredients: 1 ½ pears (approx. 180 g), cored and cut into pieces (3-4 cm); 150 g cucumber, cut into pieces (3-4 cm); 50 g green lettuce leaves (iceberg or cos lettuce); ½ lemon, flesh only, no white pith and deseeded; 1 - 2 tbsp pure maple syrup, to taste; 250 g chilled water