According to Wikipedia, the average ejaculate contains 0.7 kcal of energy. To provide your mum’s RDA of approx 2,000 kcals would require just shy of 3,000 ‘servings’. This would be quite a lot of juice – at around 3 mls a squirt perhaps 10 litres – and being mainly water would keep her well hydrated. Conversely, she might be bored, as if it were to take 20 seconds a pop, ‘deliveries’ would take some 16 hours a day. I suggest you buy her a funnel for next mother’s day – she’ll appreciate the thoughtfulness xx
You can live off of any edible liquid (juice, milk, soda, coffee, etc. Even alcohol I think, though your liver would be fucked) and never drink any just-water your entire life. You won’t be very healthy, but yeah you’ll survive.