It is advisable to visit your doctor or nearest vaccination centre to see what the required vaccinations are during your stay in Cambodia. Travel physicians may recommend you some of the listed vaccinations below: 
Hepatitis A - A food borne disease, not uncommon in Cambodia.
Vaccination: Injection series.
Tetanus
Hepatitis B - Transmitted primarily by sexual contact, shared needles and contaminated blood. Prevalent in Cambodia.
Vaccination: Injection series. 
Typhoid - A food borne disease, not uncommon in Cambodia.
Vaccination: Injection or pill series.
Japanese Encephalitis - A mosquito borne disease. Limited to parts of Cambodia.
Vaccination: Injection series.
Cholera - A food/water borne disease. Occasional outbreaks in some parts of Cambodia.
Vaccination: Injection. 
Rabies - A bodily fluid borne disease. Present in Cambodia. Generally limited to certain professions.
Vaccination: Injection series.
Malaria - A mosquito borne disease. Prevalent in some parts of Cambodia.
Vaccination: None. Prophylactic pills and/or good mosquito prevention habits.
 
Other diseases of concern:
AIDS/HIV - A bodily fluid borne disease. Prevalent in Cambodia, particularly amongst commercial sex workers. Avoid blood products except in emergencies. Practice safe sex. 
Dengue Fever - A mosquito borne disease. Prevalent in some parts of Cambodia, particularly at certain times of year. No vaccination or prophylactic available. Practice good mosquito bite prevention habits.
Worms - A food borne parasite. Eat at reputable restaurants. Practice good hygiene. Beware of street food. Beware of undercooked meat.  
Giardia, Salmonella - Food/water borne diseases. Eat at reputable restaurants. Practice good hygiene. Beware of street food.

The major hospitals in Phnom Penh include Preah Ket Mealea Hospital, which was built in 1893, the 500-bed Soviet-Khmer Hospital, Friendship Hospital, and the most renowned French-operated Calmette Hospital. 

Food and Water
Cambodia cuisine is highly comparable to the cuisine of its neighboring Thailand. The distinction, however, lies on the fact that while Thai food seems to be chilly-based, Cambodians prefer the mixed ingredients (called “Kroeung”), comprising of milder flavors of the lemongrass, galangal, ginger, and cardamom. Commonly unique Cambodian dishes include “Samlor Ma Chu Kroeung, Samlor Kor Ko, and Cha Kroeung.” Particularly, the paste fish called “Prahok” has long been a specialty for Cambodians, specifically for those living in the countryside as rice, similarly, is the main course eaten with most meals.

While you are in central Phnom Penh, the tap water is safe enough for drinking. However, we would rather always recommend you drink the bottled or boiled water throughout Cambodia.