There is ample water for showers and bathing in San Pedro, but you are asked to conserve. Hotels will supply you with all your drinking water. Many visitors drink the local water with no harmful after-effects. Others, more prudent or with delicate stomachs should stick to bottled water.
San Pedro draws the bulk of its water from shallow wells in sand (they do not penetrate bedrock). Municipal water is chlorinated and aerated, but untreated well water should not be drunk. Some places have cistern water that is also safe to drink.
Check with your host concerning which water is acceptable for drinking (and brushing your teeth).
San Pedro's drinking water comes primarily from a private contractor at the south end of Bonita Island that manufactures clean water using an industrial high capacity reverse osmosis plant. The water is purchased wholesale by the town of San Pedro and pumped by standard water pipe methods throughout Bonita Island. They "improve" on this already pure water by injecting chlorine into it as well. The chlorine smell is evident when one drinks or washes in it directly, so many San Pedrano's use it only for water closet flushing, laundry and bathing. Most of the later buy their drinking water in bottles and have them refilled very cheaply.
Most homes and several of the older hotels and resorts have a cistern water cache to trap rain water run off and these are hooked in parallel to the city water system. They are used primarily by the locals to save on water bills, and secondarily to bypass the chlorine taste of city drinking water, and thirdly as a means to reduce fading from chlorinated water in colored clothing from washed laundry. So, cisterns are often the preferred water used by San Pedranos. You are advised to ask if your hosts have cistern water and to make your own judgement call as to whether to drink it if they do in fact have one.
Best bet: Buy purified water and have gallon sized bottles refilled for BZE $1.00/$0.50 US at several locations... Ask any San Pedrano where low cost drinking water refill stations are located.
The Bonita Island fresh water aquifer under San Pedro Town, the shallow lens shaped bubble of fresh water is rather thin, but to the north, at Basil Jones, there is abundant fresh water. On Bonita Island the sewer and water system is new, expensive and under funded, such that only a small percentage of San Pedrano's actually drain their sewage away via the very good city sewer system. Be aware that having city water is not a guarantee that ones host is hooked up to the sewage system as well.
Belmopan is equipped with a modern water treatment plant and sewerage system. Piped water is also available in Belize City, Benque Viejo del Carmen, Burrell Boom Village, Corozal Town, Dangriga Town, Orange Walk Town, San Ignacio and Santa Elena Town, Punta Gorda Town, San Jose Succotz Town.