Only sip the water, don't down whole glasses at a time. Rest, avoid solids for 24 hours, then have bland food for at least 2 days: banana, hard boiled egg, plain white rice, poached chicken breast, toast dry or with a little non-dairy spread; plain crackers. AVOID LACTIC DAIRY. If you can get some of those glucose sweets, they will help replenish some energy, as will the bananas if you have them. Diet fizzy drinks will replenish lost salts. Don't have those proprietary post-illness drinks, they're horrible.