It is a kind of tankless, lager-caliber tube and low-pressure solar water heater system with the following features The system contains 4-8 pieces of vacuum tubes as one unit, with each tube capacity of 16 liters of water. this one is 5 pieces of vacuum tubes as one unit. Inside each tube, there is a high-temperature-resistant and corrosion-resistant stainless-steel cylinder made of food-grade 304/316 material, so the solar heater does not require a water tank like other products in the market, thus saving space. the heater is pressurized. It is connected to the tap-water supply system and on the other side it is connected to the shower head in the bathroom, so the pipeline is relatively simple, and the installation and maintenance are also simple and convenient. Because this water heater is connected to tap-water supply system(pressurized), it can be installed anywhere for buildings, such as on the ground, the roof, the balcony, the terrace etc., whether high-rise building, multi-story building, bungalow or villa. Each tube is equivalent to a thermos bottle, which has good insulation performance, and there is air between the steel cylinder and the glass tubes, which also provides the added thermal insulation. and the tube openings are also insulated by good materials, ensuring optimal heat retention. Based on our experiments conducted on the rooftop of an eight-story building, with daytime temperatures reaching 7C and nighttime temperatures dropping to -3C or -5C, it is observed that when 15C water was injected at 9 AM, the water temperature ranged from 51C to 64C at 17:00 PM. The following morning at 8 AM, the water temperature ranged from 42C to 47C, and by 17:00 PM, the temperature of the hot water reached 85C.